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Max Planck Encyclopedia of Public International Law [MPEPIL]

History of International Law, Ancient Times to 1648

Wolfgang Preiser

From: Oxford Public International Law (http://opil.ouplaw.com). (c) Oxford University Press, 2015. All Rights Reserved.date: 18 July 2019

Ancient Times to 1648

Published under the auspices of the Max Planck Foundation for International Peace and the Rule of Law under the direction of Rüdiger Wolfrum.

A.  Introduction

The following survey of the early history of the law of nations is confined to those periods which have proved to be of importance for modern international law. Developments which have had no noticeable influence on the modern law have been left out of account. The evolution of international law in the Far East and in South and South-East Asia are treated in separate articles. This article deals principally with European developments in the narrower sense, beginning with the international law of the ancient Greek city-States; however, it also includes an account of the legal features of an international character in the ancient Near East, whose close connection with the cultures of pre-classical antiquity is now recognized to an increasing extent (see also International Law, Regional Developments: East Asia; International Law, Regional Developments: Latin America; International Law, Regional Developments: Islam; International Law, Regional Developments: South and South-East Asia).

The article principally concerns those periods in which the law of nations played a substantial part in determining the practice of international relations (International Relations, Principal Theories). Other periods, in which individual legal features of an international nature did exist, but which did not produce a functioning international legal system, are dealt with only to the extent required by the context.

B.  Ancient Times (3000 BCE to AD 400)

1.  Pre-Classical Antiquity

Around the beginning of the third millennium BCE, the Sumerians in southern Mesopotamia and the Egyptians in the Nile valley became the first peoples to cross the threshold between prehistory and early history. Through the invention of writing and the establishment of chronology they acquired the means of recording the life of both the individual and the community and putting it into historical sequence, and thus gained a heightened awareness of their existence. Only then were the conditions created in which a meaningful and purposeful ordering of life, the development of law, and the definition of interests on the basis of law became possible.

However, international relations in the Near East in the third millennium and the first half of the second millennium cannot be regarded as being regulated by law. Egypt cannot be considered as a party to international relations at this time, since until around the middle of the second millennium it only engaged in relatively sparse trading with the Syrian coastal region and otherwise remained predominantly in the traditional isolation of the Old Kingdom until the age of Hyksos (circa 1650 to 1550 BCE). The lively dealings between the Sumerian city-States in Mesopotamia did indeed provide the external conditions for an international legal order to come into existence; however, the instability of these relations and, above all, the lack of a developed sense of legal rights and obligations meant that, here too, the evolution of an international legal order did not progress beyond an early stage. The codifications of national law, which are found from the end of the third millennium in the Near East, at first only affected the position of the individual in the State. Even a ruler such as Hammurabi of Babylon (1729 to 1686 BCE), whose care for securing the legal rights of his subjects is evident, pursued an unscrupulous policy of using force to achieve external objectives. It was only with the consolidation of relations between States in the 16th century BCE that the internal and external conditions necessary for the development of an international legal system were met at the same time.

The political equilibrium that provided the foundation for a system of international relations, based inter alia on law, in the ancient Near East from the middle of the 15th century BCE until the inclusion of the so-called ‘maritime peoples’ around 1200 BCE, involved—admittedly not precisely at the same time—five independent States of equal rank: Egypt, Babylonia, the Hittite Kingdom of Asia Minor, the Mitami from the north-west of Mesopotamia (who flourished before the middle of the 14th century BCE), and the Assyrian Empire (whose power increased as that of the Mitanni declined). These two and a half centuries were by no means free from military conflict, but the predominant impression is one of a varied international life, ranging from extensive trade and cultural contacts to frequent close links between the rulers and their families and to many legal ties. A close network of international relations came into existence, supported by a uniform international language, Akkadian, and included a number of States of lesser importance in addition to the principal powers. Although, no doubt, only a fraction of the surviving material has so far seen the light of day, archaeological evidence enables us to know more about the international relations of this period than about those of many periods closer to our own time. Such evidence includes the tablets recovered at El-Amarna in Upper Egypt from AD 1887 onwards, which provide information on Egyptian foreign policy in the first half of the 14th century BCE; the clay tablets from the archives of the Hittite capital Hattusas (modern Boghaz Keui), which have been excavated since AD 1906; the diplomatic correspondence of the local rulers that was discovered from AD 1929 onwards in Ugarit in northern Syria (modern Ras Shamra), and many other discoveries. The richest sources of information concern the international relations of the Hittite Empire.

The need felt by the Hittites in this, as in other aspects of life, to clarify their relationship with the surrounding world, led them to bring their relations with other States, as far as possible, into a definite legal order. Besides ‘allies’, on the one hand, that is to say rulers of equal rank, with whom there existed treaties of friendship and alliance (Alliances), and ‘enemies’ on the other, they knew two further forms of association between States, both based on inequality: the relationship of vassalage, which is sometimes more a matter of national public law than international law; and the position of kuiruana man, ranking between an ally and a vassal, which was legally a kind of protectorate. The rulers recognized by the Hittite Emperor as his equals—the kings of Egypt, Babylonia, Assyria, and the Mitanni—are expressly listed as equals in the texts of Hittite treaties from the end of the 14th century BCE. Only one of these treaties between equals—admittedly the most important—has been preserved: the peace treaty (Peace Treaties) of about 1270 BCE, 16 years after the battle of Kadesh on the Syrian Orontes, between Egypt and the Hittite Empire. This contained a defensive alliance, a non-aggression pact, an obligation to render assistance against rebel subjects, mutual guarantees regarding the succession to the throne, and provisions concerning extradition (Extradition; Non-Aggression Pacts). It was characteristic of a treaty concluded between equals that both parties should swear to it; the treaty was perfected by mutual obligation (lex) and attestation. By contrast, treaties concluded with rulers of lower rank than the Hittite Emperor—whether under international or national law—were characterized by the fact that, in general, the other party swore to a text placed before him by the Emperor, although he would also invoke his own gods as witnesses to his oath. In contrast, the treaties later dictated by the Assyrians were, in most cases, sworn to in the name of Assyrian deities alone, and for this reason cannot, as a rule, be considered as part of international law. The Hittite laws of war were also characterized, by comparison with what was usual in the ancient East, by respect for legality and humane behaviour. A typical example is the institution of ‘submission at the place of conflict’, which preserved a besieged town from destruction and its inhabitants from being taken into captivity.

The collapse of these States and their legal order around the year 1200 BCE was followed by several centuries of pronounced international anarchy and then, from the ninth century BCE, by the era of Assyrian supremacy, during which efforts to achieve unlimited world domination largely excluded the development of international legal relations. After the end of Assyrian rule, a new equilibrium was established in the Near East at the end of the seventh century BCE between Egypt and the Median, the New Babylonian, and the Lydian kingdoms, but this had to yield soon after the middle of the sixth century BCE to the Achaemenid Empire founded by Cyrus.

2.  Ancient Greece and Persia

International legal relations within the ancient Greek world existed from the time that the subjects of an international legal system had been created in the form of the internally autonomous, externally sovereign city- or municipality-States (polis), at the latest by the end of the seventh or the beginning of the sixth century BCE (Sovereignty). The international legal order which bound these city-States together ended with the loss of Greek freedom at the battle of Chaeronea (338 BCE). The forms of international legal relations developed in the sixth and fifth centuries BCE did indeed survive for a long time in the Hellenistic world, but where city-States were concerned, it was only in exceptional cases a matter of the autonomous regulation of international relations among independent subjects of the law, as is necessary for international law. Doubt cannot be cast on the existence of ancient Greek international law, either on the ground that this was an instance of relations between subjects of the same nationality, or even of one Hellenic ‘nation’, or because of the small scale of the relationships. The Greeks never formed a single nation in the political sense, for all their consciousness of their cultural unity; the fact that they had a common heritage never prevented them from treating subjects of other Greek States in exactly the same way as non-Greeks, or from forming alliances with non-Greek powers against their fellow Greeks. The undeniably small scale of all the relationships, however, tends not to exclude the possibility of an international legal system governing relations between equals in this instance, any more than in the Late Middle Ages; the only criterion is the legal structure of the system in question, not its size.

International legal relations extending beyond the Greek world existed in the fifth and fourth centuries BCE with the Persian Empire of the Achaemenids and, in the West, with Carthage, Etruscan city-States and the early Roman Republic. In this connection, it is noteworthy that theory prohibited both Greeks and Persians from entering into mutual legal relations on the basis of equality: the Greeks, because their literary spokesmen, both philosophers and tragedians, were no longer prepared, after the Persian Wars at any rate, to regard barbarians (non-Greeks) as legal subjects of equal rank; and the Persians because their political doctrines only distinguished between subjected peoples and those yet to be subjected, and thus did not recognize any communities beyond their own frontiers with which they could deal as equals. In both cases, in the actual practice of international law generally these difficulties were easily overlooked. The number of peace treaties and alliances concluded between Greek and non-Greek powers is large. The treaty establishing the Second Athenian League in 377 BCE went so far as to invite both ‘Hellenes and barbarians’ to join the League.

10  The most important legal forms of associations of States were the amphictyony and the symmachia. In the amphictyonies, originally religious associations with sacred objects, probably dating back to the beginning of the first millennium BCE, the institutions of the Peace of God (see para. 49 below) and the right to asylum (Asylum, Diplomatic; Asylum, Territorial) were first developed. Of greater importance, perhaps, is the influence which their constitutions had on the development of the laws of war; the obligation to impose joint sanctions against a member which had infringed the sworn rules of warfare is, in particular, of great topical interest for the modern observer. The sovereignty of the Member States was otherwise not affected by the amphictyony, which was based on a voluntary alliance. The same was true of the second form of association between States, the symmachia, which was in practice the predominant form. As a rule concluded for a specified term, that is to say for 20, 30, 50, or even 100 years, but occasionally also in perpetuity, the symmachia was a military alliance that acquired, at an early stage, the character of a comprehensive alliance going beyond the joint waging of war, but which in principle left the legal capacity of the allied city-States untouched. Not until the so-called hegemonial symmachies (Hegemony), the principal examples of which were the Peloponnesian League founded by Sparta around 550 BCE and the Delian League established under the leadership of Athens in 478/77 BCE, were they marked by a clear tendency for the leading power to restrict or remove entirely the constitutional autonomy and the members’ status as subjects of international law, so that they were allied only to the hegemon and not also with each other. In no instance was this achieved on a lasting basis. The desire of even the smallest Greek city-States for internal and external independence proved to be insuperable.

11  The lively contacts between the Greek city-States, which were interrupted only occasionally and briefly, gave rise to a considerable number of international law institutions, only the most important of which can be mentioned here. First and foremost, by reason both of the frequency of its occurrence and its importance for the settlement of differences between States, is arbitration; a system of international arbitration as highly developed as that of the Greeks only occurred again in the Late Middle Ages in the West. The law of the Greek city-States concerning aliens reached a remarkably high level; here the institution of proxeny (‘State hospitality’, from proxenos, one who takes the foreigner under his protection) is of particular interest for international law, it being the earliest form of consulate known to us (Consuls). Treaties on commerce and shipping (Commercial Treaties; Treaties of Friendship, Commerce and Navigation), coinage agreements, treaties on enforcement in the courts of many different kinds of claims (symbola), and a richly developed system of diplomatic missions (Diplomacy), together present a picture of a world that achieved an astonishingly complete and effective organization of international relations for such an early time.

12  Military conflict was, as a rule, preceded by an attempt to settle the dispute by arbitration (Peaceful Settlement of International Disputes). The conduct of warfare itself was, at least at the beginning of the era, and again during the Peloponnesian War, relentless and brutal, particularly in the treatment of the defeated—though of course this was in accordance with the cruelty of the internal penal system. Not until the fourth century BCE was there a definite change to more humane methods. In addition to armistice agreements and peace treaties concluded—as a rule for a specified period of time—in order to end a war, the international law of the Greeks also recognized ‘general’ peace treaties, that is to say, treaties, usually following a military conflict, where the parties were not limited to those involved in the conflict but included a large proportion of the other city-States, and which had the particular characteristic that, clearly following the example of the amphictyonies, they contained an obligation to join collective sanctions against a party breaking the treaty.

13  It is only natural that where relations between the Greek city-States and non-Greek powers were concerned, the most prominent features of a legal nature were those that related to war, examples being military alliances, armistice agreements, and peace treaties. However, agreements involving the law of peace were not entirely absent.

14  Evidence of the international law of the ancient Greek period has come down to us in considerable quantities in contemporary literature and in—admittedly only fragmentary—inscriptions. From this we can see that agreements were only effectively binding on the contracting parties when the parties had sworn to them by the deities under whose protection the oath was taken. In this case, the ceremony was not simply an ornamental addition, any more than in the treaties of the ancient Near East. Indeed, the sacred rite frequently gave its name to the act: to ‘pour out the libation’ meant to conclude the treaty.

3.  Romano-Hellenistic Period

15  It is not easy to answer the question as to when the Roman Republic began to maintain lasting international relations of a legal nature with other States. We can only be certain that Rome’s international legal relations do not, at any rate, date back to the first treaty with Carthage (around 500 BCE). This agreement, the content of which has come down to us from Polybius (book 3 chapter 22), demonstrates that that age was not yet able to look beyond the mere delimitation of areas of power to the legal regulation of international relations. Moreover, Rome’s power—which at that time did not extend beyond Latium—was so seriously weakened soon after the conclusion of the treaty that for a long time Rome ceased to be a party to any significant international agreements. It was only after consolidation of the internal situation through an initial accommodation between the estates (the Twelve Tables; re-organization of the peasantry; creation of the comitia centuriata) around the middle of the fifth century BCE that the necessary conditions existed for renewed external political activity. Whether the increased military conflict and treaty relations with the Aequi, with the Volsci and particularly with Etruscan city-States, which followed in the final third of the century, can be regarded as the beginnings of an international legal order—limited at first to central Italy—can be left open. In the fifties of the fourth century BCE at the latest, however, the Roman Republic was a participant in a fully developed system of international law, the scope of which extended far beyond central Italy. The most important dates, which also give some idea of the intensity of the international involvement, were: 358 BCE, renewal of the treaty with the Latins and the Hernici; 354 BCE, foedus aequum (equal treaty) with the Samnites; 358 BCE, hundred-year peace with Etruscan Caere; 351 BCE, permanent armistice treaties with two other Etruscan city-States, Tarquinia and Falerii; 348 BCE, the second treaty with Carthage; 343 BCE, foedus aequum with Capua; and so on. The sequence was sometimes broken by military conflict on a comparatively large scale, as with the Samnite tribes, for example, and later with Carthage, but in general we find a constant and inexorable extension of the list of parties to international agreements.

16  The year 338 BCE marked the first identifiable stage in the development of this international legal order, when the Latin communities in their various constitutional and international forms were finally bound to Rome. The second stage was reached shortly before the outbreak of the first Punic War. Here the year 265 BCE marked the completion of the unification of the mainland under Roman leadership in the Italic League; this then became the fifth and youngest great Mediterranean power besides Carthage and the three Hellenistic successor States of Macedonia and the Kingdoms of the Seleucids and the Ptolemies, which had all coexisted since about the year 280 BCE in a state of reasonably well-consolidated equilibrium. The third and final stage dates from the end of the second century BCE, when Rome had removed its rival in the West, Carthage, and begun to deal with the powers in the East.

17  This last period in which a functioning system of international law existed to some degree in the Roman world admittedly lasted no longer than a human lifespan: after Macedonia broke up following the battle of Pydna (168 BCE) and the Seleucid king, Antiochus IV, was humiliated before Alexandria in the same year, there was no longer a system of independent States of equal rank—the first condition for any form of international law—in the Eastern Mediterranean either (Mediterranean Sea). Even though the Romans at first recoiled from taking the huge territories of the East directly into their possession and administration, their unlimited authority was no less undisputed because of that: ‘From this time on the whole civilized world recognized in the Roman Senate the highest court of law, the commissions of which decided in the final instance between kings and peoples’ (Mommsen). International law based on equality of the subjects of the law was replaced, first by a system of alliances dictated by Rome, and finally by the provincial system. This did not prevent the occasional use of the old forms of international legal relations well into the imperial era, the principal examples being the agreements made with the Parthian Kingdom of the Arsacids during the late republican period until the end of Arsacid rule (AD 226). These were not, however, part of a continuous legal order among equals, for even though the Parthians were in practice independent throughout this whole period, Rome never deigned to accord them the status of equals. It was on the whole no more than a game—at times deliberately played as such, under Claudius, for example—with the traditional forms of international law, which only began to receive proper substance again as the new Persian Empire of the Sassanians, the successors to the Parthians, gained in strength and grew to be the only serious partner for Rome during the time when Rome ruled the world.

18  There can no longer be any doubt that the Roman world also had an extensive area of law which could be called, in modern terminology, the international law of peace, now that scholars have abandoned the idea—which Seckel rightly called ‘as unhistorical as it is unrealistic’—that the States of antiquity lived in a permanent state of war with each other (Peace, Breach of). ‘The fundamental relationship ipso iure between the peoples of the ancient world’ was, as Seckel (differing from Mommsen and most scholars) convincingly showed as long ago as 1915, ‘not enmity between States, but on the contrary peace, pax, the condition in which there is “neither war nor friendship nor hospitium nor an alliance” (Digest 49, 15, 5 para §2) between peoples’. One must, however, note that the relationship of friendship between States (amicitia) arose automatically, without the need for an express treaty or any particular formality, ‘through any kind of non-hostile intercourse between Rome and a foreign State’ (Heuss 1933). The relationship with the friendly State could then be expressed in treaty form through either a foedus aequum (a defensive alliance with mutual obligations to provide military assistance) or a foedus iniquum. This ‘unequal alliance’ imposed obligations on the other party alone: the duty to serve under Rome’s command even in wars of aggression and to respect the supremacy of Rome (through the inclusion of the maiestas clause: ‘maiestatem populi Romani comiter conservato’); this meant that Rome’s ally in a foedus iniquum lost the legal position of a sovereign State, at any rate in relation to third States.

19  Among the other forms of treaty found in the international law of peace, the most important was that of hospitium (hospitality) and the general rules of law governing aliens connected with it; many different forms of constitutional and international relationships developed by which the earlier Republic bound the Italic city-States to itself. The institution of deditio, by which a foreign community submitted unconditionally to Rome, applied particularly to surrender in war, but subjection could occur in practice without any preceding military conflict with Rome as, for example, when the State surrendering was threatened by another, more powerful, State and preferred to submit to the Romans. The unilateral act of surrender was usually followed by the conclusion of some form of treaty.

20  Rome never developed arbitration as we find it in the international law of the Greeks. The Roman Senate acted as judge often enough in disputes between third parties, but Rome was never prepared to allow an arbitrator to decide where its own affairs were concerned. By contrast, the practice of diplomatic missions attained a position of particular importance in the international law of the Roman world. Although the Romans did not maintain permanent legations, nevertheless the idea that the representative of another power should be regarded as sacrosanct under all circumstances and without any specific prior agreement, an idea which was merely hinted at in Greek international law, first gained complete acceptance with the Romans (Immunity, Diplomatic). They not only maintained this principle strictly themselves, but also expected others to observe it and reacted sharply when their own representatives were not treated in a proper manner.

21  The central concept of the Roman laws of war is that of the bellum iustum or pium. A war was not ‘just’ in the Roman view merely because it had been declared in the prescribed form; it was further necessary that it should rest in fact on a iusta causa. According to Cicero (De re publica 3, 23) this condition was only satisfied if the war was waged to avenge a wrong suffered at the hands of the enemy or in self-defence: ‘extra ulciscendi aut propulsandorum hostium causam bellum geri iustum nullum potest’. This late definition is entirely in accordance with what we know of the position in earlier times from other authors, such as Livy, and its substantive requirements are certainly no different from those followed in practice from time immemorial. According to principles which had been developed at the time of the early Republic, the formal requirements for the declaration of war were twofold: demanding reparations or satisfaction from the other side (rerum repetito) and, if the demand was not met, a formal declaration of war (indictio belli) (Reparations). The latter was made in traditional form by a priest of the College of Fetials, to whom the conduct of legal relations with foreign countries was in general entrusted, since this was done in strictly religious form.

22  The most important question in the law governing the conduct of warfare was that of the treatment of conquered cities (Warfare, Methods and Means). If deditio occurred before the battering ram touched the principal wall, at least the lives of the male population were frequently spared. There was, however, no binding rule to that effect. When New Carthage was taken by storm in 209 BCE, Scipio the Elder set the inhabitants free immediately, except for the most menial workers, who were declared to be the property of the Roman people for the duration of the war. On the other hand, in 107 BCE, in the Jugurthine War, Marius had all men who were fit for military service in the south Tunisian oasis town of Capsa put to death in spite of the surrender—though this was admittedly contra ius belli, as the historian Sallust observed (Bellum jugurthinum ch 91). The legal position of the Roman citizen who became a prisoner of war was more clearly defined (Prisoners of War). He lost his personal rights, indeed his legal capacity generally, but if he crossed the frontier again after his release all his rights revived retrospectively by virtue of the right of postliminium.

23  War was ended either by occupation (Occupation, Belligerent) or by the conclusion of a treaty (Occupation, Military, Termination of). Occupatio was a unilateral act which entailed the legal destruction of the defeated State (Debellatio); its territory was taken into the Roman imperium (Annexation) and, in cases of doubt, its inhabitants were accorded the legal status of peregrines. In earlier times, the termination of war by treaty not infrequently involved a long-term armistice, concluded for a period of 2, 3, 6, or up to 100 years, which was sometimes, though not regularly, followed by a formal peace treaty. Short-term armistices were concluded by the military commander alone in the form of a sponsio. Peace treaties, however, required the approval of the people. If, after the conditions had been approved or amended by the Senate, the popular assembly sanctioned the treaty prepared by the military commander, a formal law then came into existence, which the Fetials had to put into the form of an oath. As soon as the appropriate priest of the opposing State swore the corresponding oath, the treaty entered into force without any possibility of withdrawal: the double oath was the conclusion of the treaty.

24  The official term for the law of nations was ius pacis et belli. However, the designation ius gentium (occasionally ius alone) occurred not infrequently, particularly in the writings of historians; the almost exclusive use of the latter term in the Middle Ages and modern times in the sense of international law is thus not so incorrect as is sometimes asserted.

25  The high level of legal refinement of international relations in the Roman world is obvious, even on a fleeting comparison with the relations between the Greek city-States. The question is whether they were based upon the conviction of those concerned that the rules were principles of a legal order, which the parties were legally obliged to observe while recognizing each other as equals, and the infringement of which entailed legal sanctions. An affirmative answer can definitively be given for the earlier period until about the beginning of the first Punic War (264 BCE) and also, with certain reservations, for almost another century, down to the battle of Pydna (168 BCE). The desire for self-assertion, which was never seriously shaken off, was at first, in the early centuries of the Roman Republic, in no way directed at obtaining unrestricted power. Indeed, it did not prevent the States with which the Romans came into contact, whether friendly or hostile, from being considered as independent subjects of equal rank under the law, with which legal relations were thus possible on the basis of equality. The fact that Rome was only prepared to recognize other powers as sovereign equals in exceptional cases after the defeat of Carthage, and that it was not prepared to recognize them as such at all after the battle of Pydna, rests on the complete change in circumstances, which from then onwards excluded the possibility of international law on the basis of equality. However, mutual confidence that agreements would be upheld must, at least until the end of the third century, have been greater than in some later periods for which the existence of a system of international law is accepted without hesitation; only after the second Punic War did the Roman fides begin to lose its old reputation, at least in the area of international relations.

C.  Transition from Antiquity to Middle Ages (AD 400 to 800)

26  It is more difficult to draw even an approximately accurate dividing line between ancient times and the Middle Ages in the history of the law of nations than it is in history generally. The period in which the ancient forms of life gradually died out while the features which are characteristic of the Middle Ages became even more prominent— roughly from AD 400 to 800—cannot correctly be counted either as part of late antiquity or as part of the Early Middle Ages. It is decidedly a transitional period.

27  The turn of the fourth century is important in several respects for the history of the law of nations. In the East, the new Persian Empire of the Sassanians had attained such a position of strength through a series of wars against the peoples on its eastern borders and against Rome, which wars occupied the major part of the third and fourth centuries, that Theodosius I was forced to conclude a treaty with Bahram IV around AD 389, thereby dividing up the Armenian territory which was the principal object of dispute. From that moment on the Roman Emperor and the Sassanian King stood side by side as independent sovereigns who respected each other—de facto at any rate—as equals. In AD 395, the Roman Empire was itself divided, after the death of Theodosius, into an Eastern and a Western part. This kind of division was nothing new in the history of the late Empire. The intention was also to divide the administration while securing the cohesion of the Empire by having a single ruling dynasty. This proved insufficient in the face of the irresistible force of circumstances: notwithstanding all the efforts of later generations, the Empire was never reunified. Internal developments provide part of the explanation for this, but the principal cause of the continuation and even extension of the division lay in the growing incursions by Germanic tribes into the territory of the Roman Empire towards the end of the fourth century, in the so-called migration of peoples.

28  The Eastern part of the Empire was able to resist the invaders in the end, but not without serious losses of life and territory. The West largely succumbed to the invaders. The abandonment of, and withdrawal from, Britain in the first decade of the fifth century, the repeated invasions of Italy by the Visigoths under Alaric (in 401 and again from 408), which led in 410 to the fall and sack of the ancient capital of the Empire—not entered by an enemy for eight centuries—made the inability of the Western Empire to resist disintegration plain for all the world to see. Thereafter, it was only a question of time until the first Germanic kingdoms arose on the territory of the Empire: the Burgundians on the Middle Rhine in 413, the Tolosan Visigoths in south-west Gaul in 418, and the Vandals in North Africa in 429. The political picture of the Western part of the Empire was thus fundamentally changed soon after the turn of the century, even though the imperial government at first succeeded in keeping these States in the legal position of foederati.

29  The beginning of the ninth century marked the end of a stage in these historical developments. By then the new Persian Empire, which for centuries had been the Roman Empire’s rival in the East, had long since disappeared. Its place had been taken by the new and expanding power of the Empire of Arabic Islam. The battle for survival fought between Islam and the Eastern Empire for more than a hundred years ended essentially when the Abbasids won the caliphate in the year 750 and soon afterwards moved their capital from Damascus to Baghdad. The two powers of the East were joined by the Kingdom of the Franks as the leading power of the West after the collapse of Eastern Roman rule in Italy (751) and the final defeat of the Lombard Kingdom (774). Charlemagne’s assumption of the title of Emperor in the year 800 and his recognition as Emperor of the West by the Eastern Emperor Michael I in the Treaty of Aix-la-Chapelle (812) are indicative of the supremacy of the Frankish Empire, which in turn had maintained diplomatic relations with Caliph Haroun al-Rashid since the year 797.

30  The transitional period was not able to develop a lasting and comprehensive legal order for a world which now extended considerably beyond the Mediterranean area. It did, however, have a substantial number of particular international legal features, some of which had an influence on the law for a long time to come.

31  As far as the Roman Empire’s relations with the Sassanians are concerned, the division of Armenia towards the end of the fourth century removed the principal point of conflict between the two powers, and thereby ushered in a period, if not of peace, at any rate free of hostilities, which lasted for practically the whole of the next hundred years. The sixth century, and the first half of the seventh century, on the other hand, were again filled with long and difficult struggles which, without leading to decisive changes in possessions or power, so exhausted both empires that they were incapable of putting up sustained resistance to the Arab advance after the death of Mohammed (632). The Sassanian Empire succumbed completely to Islam around the middle of the seventh century; in the same decades the Roman Empire lost its most valuable possessions in Asia and Africa, but, although its existence was at times seriously threatened, it succeeded in maintaining its position at least in its central areas of Europe and Asia Minor.

32  The long period of military inactivity between the Roman Empire and Persia contained few events of an international legal nature; the period of renewed military conflict which followed proved to be all the more productive in this respect. The principal feature was the extensive diplomatic intercourse. Although, in spite of its unusual intensity, it still did not lead to the creation of permanent legislation, it bears comparison with the developed diplomatic style of later times in its scope, practical importance and formal features. Of particular interest in this respect is the form of address (‘Brother’) used by the rulers to emphasize their equality. This is the same expression as the one which was customary in the Orient in antiquity among rulers of equal rank, and modern Byzantine research leaves hardly any doubt that this is a case of a name and a concept being passed on unchanged in substance—from the Achaemenids through their Hellenistic successors, the later Roman Empire, the transitional period, and mediaeval Western Europe—down the ages to the dawn of the modern era.

33  Among the peace treaties of the period, the perpetual peace of 532 and the 50-year peace of 562, both concluded between the two most important rulers of this epoch, Justinian I (527 to 565) and Chosroes I (531 to 579), are of particular significance. No ‘peace without end’ had previously been concluded between the two powers. The reason for doing so at that time was presumably that it was desired by the Persians, who thereby hoped to secure, for an unlimited period, the annual payments made by Rome towards the defence of the Caucasian passes against the Central Asian tribes of horsemen who threatened both empires. In actual fact the peace lasted for less than a decade. In 540 the Persians invaded Syria again. The Roman Emperor, whose best troops were stationed in Italy, was forced to accept a five-year armistice, which was extended on several occasions. It was not until 562 that a comprehensive new peace treaty was signed, which, in accordance with Roman custom, was concluded in the traditional manner for a specified period of time, namely 50 years. Only a few of the characteristic provisions of the treaty can be mentioned. Firstly, it is noteworthy that the peace treaty extended to a not inconsiderable degree beyond the frontiers of the contracting parties, the loosely organized ‘States’ of Arab tribes in the no man’s land west of the Euphrates, although they did not participate formally in the conclusion of the treaty. Further, overland trade was regulated in detail, thus building on earlier agreements and long practice in some cases; this was also the subject of exhaustive domestic regulations in the two States, designed to secure the State’s monopoly. Another noteworthy feature is the different treatment accorded to refugees and prisoners of war, which is surprising by modern standards, but of interest precisely for that reason. Whereas refugees, who mainly included prominent Armenians, were granted free return and assured of complete immunity from punishment by both governments, prisoners of war on both sides were mercilessly abandoned to their fate—a regression to profoundly inhuman customs—which one might have supposed to have been long overcome and which, on the Roman side at least, was contrary to the practice of Augustus nearly 600 years before in relation to the Sassanians’ Arsacid precursors.

34  No less interesting are the provisions of a special treaty, concluded at the same time, to regulate the legal position of the Christian subjects of the Persian king. The unrestricted freedom accorded to them in the practice of their religion is all the more astonishing, since the Christian custom of burying their dead must necessarily have seemed highly offensive to followers of the Zoroastrian religion. However, the Emperor undertook for his part not to admit religious refugees in future and, where necessary, to return them; this circumstance may have induced the Persians to undertake such a far-reaching obligation of tolerance. Until recently, Arts 7 and 11 of the treaty were interpreted as showing agreement for the settlement of disputes by a permanent court of arbitration; the latest research has, however, demonstrated that this is merely a chimera (Judicial Settlement of International Disputes). Correctly interpreted, the two articles provide for the possibility of preventing the outbreak of an international conflict by opening national courts to foreigners, which is notable enough in itself.

35  Islamic theory of international law after the end of the great conquests and the consolidation of power under the caliphate of the Abbasids successfully sought to work out the conditions under which legal relations with non-Muslim States could be conducted, without infringing the traditional religious provisions. The most important legal agreements regarded as permissible were the assurance of safety (aman) developed from the ancient Arab law of hospitality, which provided the basis for the law of diplomatic missions, and the alliance between equals (muwada’a), although the latter was only permissible where the Muslims had been defeated by the unfaithful, and if not concluded for a stated time only, could in any event be unilaterally terminated at any time. In the High and Late Middle Ages, however, both sides, Islamic as well as Christian, went far beyond the limits set by their respective religions in their practice of international law.

36  The obvious question as to whether a fragment of a system of international law corresponding to the partial legal order of the East is, at the same time, to be found in the Western Mediterranean area can only be answered by looking at the constitutional and international legal status of the Germanic tribal principalities, which had arisen on the territory of the Western part of the Empire. Here the position differed too much from case to case for any uniform development to have taken place. Weaker armies or tribes never progressed beyond the relationship of a foedus iniquum. In other cases, where greater strength of numbers combined with advantages of time and place, skilful generals succeeded in advancing beyond the status of foederati to independence. Thus, in the peace treaty of 442, the Vandal Gaiseric was recognized by the Western Emperor Valentinian III as sovereign ruler of the North African coastal area conquered by him, and in 475 Euric achieved legal independence, even if only for a limited time, for the Visigoth Kingdom in southern Gaul. The best known Germanic ruler of this period, the Ostrogoth Theodoric, who was the de facto sole ruler of the central areas of the West after the removal of Odovacar (493), was no more than a constitutionally dependent rex in relation to the Emperor. The coins minted in Italy during his rule bear the image of the Emperor, with Theodoric’s monogram on the reverse. The Emperor reserved the right to enact leges and Theodoric ruled by means of edicts in the manner of a Roman civil servant. Only the Emperor, not Theodoric, had the power to confer Roman citizenship. Whether the Germanic king’s authority was legitimate for external relations, as it was internally, depended on the Emperor alone: only after repeated urgent requests did Theodoric finally receive the ‘ornamenta palatii’ from Constantinople in 498 as a sign of the legality of his royal position.

37  In the case of the Franks, whose empire alone endured, everything points to the immediate achievement of unlimited independence: the favourable relationship of the numbers of the immigrants (Immigration) to those of the native population in the areas to be settled; their remote location, seen from the centre of the Empire; the proximity of their previous territory and the possibility of supply; unweakened national strength; and the leadership of an unhesitating genius. In these circumstances, it practically goes without saying that they did not take over the system of foederati, which until then had prevailed in Gaul, with legal consequences for the division of the country; they behaved as freely in their external policies as they considered possible in each situation. This does not alter the fact that in principle they never questioned the constitutional supremacy of the Emperor. The only exception to this was Theudebert I (543 to 548), who was the first Merovingian king to claim the full right to mint his own coins and who also sought in other respects to establish his equality, as ‘Augustus’ of the West, with the Eastern Emperor. The decline of the Merovingian dynasty began immediately after Theudebert prevented this line from being pursued further. This final example also shows that the first requirement of a fully formed and functioning international legal order, namely the simultaneous existence of independent subjects of international law, was not satisfied in the West in this period.

38  The importance of the transitional period for the history of the law of nations lies not least in the fact that it produced the first results of the process, begun in the early centuries of Christianity, of revising the legal ideas of antiquity affecting relations between States to accord with the spirit of the new religion. St Augustine of Hippo (354–430), one of the last and at the same time the most important of the Latin Fathers of the Church, lived at the beginning of the period, although he was not able to exert any lasting influence on the views held at that time with regard to international law. As far as the anarchy, which to a large extent took over the international practice of the West, permits one to form a judgment, the customs inherited from heathen antiquity continued to be applied at first. St Augustine’s ideas had all the more effect on the theory of international law in the later Middle Ages and in modern times. His original contribution consists not so much in the development of a Christian natural law (Natural Law and Justice)—in this area he in essence only put into systematic order what St Paul and Origen had taken from Stoic thinking on natural law and worked into the new theory—as in his new ideas in relation to the concept of peace in general, and the laws of war in particular (the principle source is De civitate Dei, written between 413 and 426.) His ideas form the basis of the conditions necessary for a just war that were laid down by the scholastics of the 12th and 13th centuries; the earliest provisions for the Christian conduct of warfare are derived from him; and he was the first to reject the doctrine that the outcome of a war was unequivocal evidence of the justice of the victor’s cause, a judgment of God, in other words—a doctrine that had been followed almost without dissent for thousands of years. That the idea of the vanity of all human endeavour constantly breaks through and that true peace is only to be expected in the next world, is only natural for a thinker living in an age governed by eschatological ideas.

39  Among the important writers of this period beside St Augustine, St Isidore of Seville (Bishop from 600 to 636) should be mentioned. His Etymologiae, an encyclopaedic collection of the learning of the time, was to be found in nearly every monastery library in the Middle Ages, and he introduced the study of the Roman legal tradition—which had gained recognition due to a number of rules of international law being included in Justinian’s codification—to the Fathers of the Church. St Idisore’s definition of ius gentium is based on this tradition and remained influential for a long time (Etymologiae book 5 ch 6): ‘Ius gentium est sedium occupatio, aedificatio, munitio, bella, captivitates, servitutes, postliminia, foedera pacis, indutiae, legatorum non violandorum religio, conubia inter alienigenas prohibita. Et inde ius gentium, quod eo iure omnes fere gentes utuntur’ (‘The law of nations comprises the occupation, building and fortification of places of residence, wars, captivity, servitude, postliminium, peace treaties, armistice, the principle of inviolability of ambassadors, and the prohibition of marriage with foreigners. This is called the law of nations because it is used by nearly all nations’; translation by the author).

D.  Early and High Middle Ages (800 to 1300)

40  At the beginning of this period of broadly 500 years there existed a single large empire of the West. By the end of the period, however, in the West of the then known world, a number of ‘nation States’ of equal rank as subjects of an international legal order had come into being. Although this legal order has been greatly extended in scope during the subsequent six and a half centuries, it has not changed its basic structure at all.

41  The Frankish Empire, which reached the height of its power under Charlemagne (768–814), was not a universal State of the same kind as the Imperium Romanum under the Emperors; with the Eastern Empire and the Islamic Empire it was faced with two rival Great Powers. However, it is important to realize that, although Charlemagne was the most powerful ruler in the West, he was not the sole ruler even there, since not only had the Ommeyad Empire in Spain successfully resisted him, but also Asturias in northern Spain and the Anglo-Saxon Kingdoms among the Christian powers did not belong to the Frankish Empire. The scope for the development of a system of international law based on the sovereign equality of its subjects was, however, relatively small at the end of the eighth century and the beginning of the ninth century, and the internal constitutional problems of the enormous Western Empire outweighed the international aspects both in size and importance. Matters changed as the Carolingian Empire began to disintegrate. The most important event in this process, which lasted throughout the ninth century, was the Treaty of Verdun of 843, under which the succession was divided. This was not at all the result of a desire for national separation, but it was an essential condition for the independent development of French and German realms. The process seems to have been rapid at first. As early as 921, a treaty of friendship was concluded between the first Saxon King, Henry I and the Carolingian Charles III, the ruler of the Western Empire, which was based on the principle of complete equality of the parties and has been rightly called the first treaty, in the proper legal sense, between the two powers. There was, however, still a long way to go before the stage of a fully developed sovereign State in the sense of the later Middle Ages and modern times was reached. Even in the West Frankish Empire, which, through its many natural advantages, was the first part of the western world to become a unified State, the process of creating a territorially self-contained, sovereign State and securing it against the set-backs which occurred was long and laborious. The obstacles to the formation of European nation States were too great. The disintegration of the Carolingian Empire was not enough to cause separate States to spring up fully fledged. The end of the Roman Empire did not mean the end of the tendency to try to unify the West into a single whole. The two competing powers, the Western Emperors and the Papacy, maintained this tendency in the following centuries. It was not until these two representatives of the universalistic idea were decisively weakened towards the end of the High Middle Ages that the way opened for the formation of a system of nation States, following in point of time the opposite tendency towards disintegration.

42  For the purposes of international law, the principal question is whether the existence of the two dominant powers excluded the possibility of other independent powers coming into being in the High Middle Ages. There is no doubt that it did not. Considering first the Western emperors, at no time, not even under the Hohenstaufen dynasty (1138–1254), did their rule extend to an area comparable with the position held by Charlemagne around 800. The only areas which were securely incorporated into the Empire were Germany, Burgundy and the greater part of Italy. The Western powers—France, England, and the Christian kingdoms of Spain—developed largely independently of the Empire. Even when their rulers respected the Emperor’s higher rank (auctoritas), they were in no way ready to let him share in their autonomous, independent power (potestas). Nevertheless, the Empire stood as a powerful block at the centre of the West, occupying too dominating a position for a society of free States to be able to form and assert itself beside the Empire’s claim—never completely abandoned—to world dominion. It was the collapse of the Empire after the death of Henry VI in 1197, which opened the way for the creation of a system of European States, the members of which—the ‘nation States’ of the West and the territories of the Empire that became largely autonomous in the course of the 13th century—grew by the end of the century from loosely-formed, mainly feudal kingdoms under Christian rulers to properly organized States, with administrations controlled from the top and relying on a dependent body of government officials.

43  By this time the second universal power in the West, the Papacy, had also long been deprived of any possibility of enforcing claims to comprehensive rule, even in the western world. At the beginning of the century, under Innocent III (1198–1216), the power of the Papacy might have appeared to have equalled, or even surpassed, the secular power of the Emperor. The reality was different, however. Although the Papacy was at the height of its secular power, all its threats of spiritual and temporal penalties could not prevent Venice, the most important commercial centre of the time, from entering into political and economic relations with the non-believers, from the turn of the 13th century onwards. Notwithstanding the almost constant state of war which existed between the Christian West and the Muslim powers, these relations became, if anything, more intensive thereafter. It was a considerable set-back for the Papacy’s idea of a single Christian orbis terrarum when the fourth crusade not only failed to reach its objective, the Holy Land, but ended in 1204 with the Christian city of Constantinople being stormed by Christian crusaders and ruthlessly looted. These are merely two illustrations of the way in which the States of the West began to break with the Church’s aims in the 13th century. At no other time did the process of secularization of the State, whose leaders now claimed for themselves the direct authority under God which they had previously conceded to the Emperor, advance so relentlessly as in the 13th century. The catastrophe of Boniface VIII in 1303 was only the visible conclusion of a development that was basically complete long before that.

44  During the period around 1300, the European State system did not posses all the features of the developed modern system, however. The claims of the old universal powers to rule were asserted—not always unsuccessfully—until the beginning of the modern area. The stabilization of territorial boundaries and the exercise of sovereignty were long retarded by the tenacious survival of the feudal system of personal obligation. The ‘impermeability’ of the modern State, which concentrates all jurisdiction in itself, though anticipated by the Normans and by Frederick II in southern Italy to a certain extent, was scarcely possible from a purely technical point of view in the large expanses of Northern Europe, and in any case did not suit an age which did not yet have the ideal of an easily governable uniform mass. Nevertheless, the decisive step towards the formation of the modern State, the development of the idea of unlimited and illimitable sovereignty, had already been taken in the 13th century both in theory and in practice. The formulae rex, qui superiorem non recognoscit in terris and rex imperator in regno suo occur throughout the religious and secular literature, in collections of laws and in diplomatic correspondence from the middle of the 13th century at the latest, and it is clear from any examination of the international exchanges of the period that those concerned did not regard them as empty phrases without binding force.

45  The law of international agreements of the period contained genuine international law, as far as relations between the recognized world powers of the Early and High Middle Ages are concerned. Diplomatic contacts between the Eastern and Western Empires were very frequent, apart from a few brief interruptions, until the establishment of the Latin Emperors in Constantinople in 1204. These contacts and those between the two Christian empires and the leading Islamic power of the day (or its rivals) led, on numerous occasions, to the conclusion of international treaties. The agreements between Christian and Islamic powers are of particular interest: some related to a long-term armistice, exchange of prisoners, and rights to pass through territory held by the other party; some contained undertakings of neutrality (Neutrality, Concept and General Rules); they frequently also involved a regular treaty of alliance, although such a treaty was contrary to the religious precepts of both sides and was designated an impium foedus by early Christian writers (Alliances).

46  In the case of the ‘political treaties’ which were concluded during the same period within the western world, on the other hand, it is sometimes difficult to decide whether they should be considered as part of international law, or merely as internal legal acts. The line between national and international law was fluid throughout the whole period. The confoederatio cum principibus ecclesiasticis of 1220, by which the spiritual princes were granted extensive sovereign rights, and the statutum in favorem principum of 1231, by which the secular princes received the same rights, are typical examples of this kind of agreement on the borderline between the two areas of law. They cannot be placed beyond all doubt into either one or other of the categories developed centuries later by legal writers. The list of subjects of international law was at all events not limited to the Emperor, the Pope, and the rulers of the rising major territorial States, but also included powers of lesser rank, as participants in international relations among equals, since the right to order both internal and external affairs as a sovereign was not regarded in the Middle Ages as being in any way dependent upon having the highest rank. It was almost the rule in those areas in the centre of Europe which were largely free of the influence of the Great Powers and which were culturally the most advanced—northern Italy, Switzerland, south-east France, and a little later south-west Germany—that rulers (both secular and spiritual) of small and medium-sized territories, provinces, cities, and municipalities, dealt with each other, or with their overlords, as autonomous ‘sovereigns’ with unlimited power. This was the exception in the central areas of the large States that were coming into being and which, in intention at any rate, followed a strictly centralized system of administration.

47  The best examples of the extent to which these ‘sovereigns’ of very different rank were treated as equals are provided by agreements on the settlement of disputes by arbitration, a practice which reappeared in the High Middle Ages after a long absence. Significantly, it was again in the central areas of Europe that the idea of arbitration extended to all branches of the law in the course of the 12th and 13th centuries, including, in particular, those branches which, in modern terminology, fall under public law and international law. Arbitration agreements also occurred elsewhere, and occasionally even between the Great Powers of the time; but these were exceptions only, by comparison with the regular and evidently quite natural appointment of an arbiter arbitrator seu amicabilis compositor for the settlement of disputes in the treaties between second and third rank powers. Arbitration flourished, in the form both of ad hoc and permanent arbitral tribunals, until the end of the Late Middle Ages, and from the 13th century onwards made ever-increasing use of formulae borrowed from canon law. In numerous cases the Pope, or a papal legate, was appointed arbitrator, a practice which is explained by the special authority inherent in the award of such a tribunal and also by the fact that, in certain circumstances, compliance with the award could be enforced by means of the spiritual penalties at the disposal of the arbitrator himself. Attempts by Innocent III and Boniface VIII to enlarge this practice into one of compulsory arbitration by the Pope for all international disputes came to nothing, however.

48  By its very nature, the principle of mutual personal obligation, which is the characteristic distinction between feudalism and all other social orders, knows no fixed territorial boundaries. It consequently impeded the consolidation of ‘nation States’ as subjects of the newly developing society of States to such an extent that it categorically demanded countermeasures. Thus, in 1244, St Louis (Louis IX of France, 1226–70) decided that he had to compel those of his vassals who were at the same time feudal tenants of the English Crown to choose between their two allegiances, and in 1258 he extended this to the French holders of fiefs in Aragon. In a number of respects, however, feudalism provided ‘the intellectual framework for international relations’ (Mitteis 122). The Papacy played a significant part in international law in this area too, in that papal recognition—given as a rule in the form of infeudation—was required before a newly formed State existed lawfully. The best known example of this is the recognition obtained by the Norman King for his rule over southern Italy and Sicily in the peace treaty of Benevento (1156), where the supreme feudal lordship of the Curia with regard to these territories is assumed without question.

49  In addition to the settlement of disputes by binding arbitral awards, the maintenance of peace was furthered by the institutions of the Peace of God (Treuga or Pax Dei) and the public peace. The Peace of God, which was first established by the Church towards the end of the 10th century in southern France and quickly spread from there both to the north and to the east, required the observance of a truce during the ‘Passion days’ of the week, ie from Thursday night to Monday morning, on pain of ecclesiastical penalties, and also created a special peace for certain persons and places. It became important for international law in connection with the crusades, which were conceived as supranational undertakings, and the failure of which promoted the separate development of individual States in the West. The attempts by the Popes, first made at the Council of Clermont (1095) and then repeated on several occasions during the 12th century, to expand the rules of the Peace of God into a general law binding on the whole of Christendom—not merely rules applying within a particular State—made little progress. Nevertheless, although it produced no practical results, this first attempt to create a law of war for the whole of Europe, characterized by the spirit of humanity and mercy for non-combatants, is of great interest for the history of the law of nations (Civilian Population in Armed Conflict; Combatants). Outstanding among the declarations of public peace—in which the State, to a certain extent, followed in the footsteps of the Peace of God movement—were those which applied to the whole Empire; Frederick I began his rule with the great public peace of 1152. Without doubt, both institutions helped to maintain peace beyond the boundaries of the territory for which they were declared, and to that extent one can say that they had an international legal effect. However, their real purpose—leaving aside the universalist ambitions of the Papacy—was to put a stop to unlawful feuds and to combat criminal behaviour within the territories concerned, and they were thus essentially national, not international.

50  The canon law theory of the prerequisites for a state of war and the rules for its conduct became important in the laws of war of this period. This theory was first expounded by Gratian (around 1140–50) and then systematically and with particular clarity by St Thomas Aquinas in the following century (around 1270). Both writers base their reasoning intensively upon St Augustine’s discussion of the subject. This applies particularly to the doctrine of the just war, which formed the core of the Christian international law of war. According to Gratian (Decretum, pars 2, causa 23) waging war is not a sin, provided that the war is a just one. Just wars are, firstly, wars undertaken in self-defence and, secondly, wars undertaken in order to punish a wrong committed by the other party. The justification for the latter type of war comes from the New Testament (Romans 13, 4: ‘But if you do wrong, be afraid, for he [who is in authority—here referring to the party waging war justly] does not bear the sword in vain; he is the servant of God to execute his wrath on the wrongdoer’).

51  St Thomas, for his part, stated the requirements for a just war in three points (Summa Theologica, Secunda Secundae, Quaestio 40): the war must be declared by a sovereign prince and waged by his order; the other party must have provided a iusta causa for the war by culpable conduct; and, lastly, to be able to rely on the iusta causa to justify the war, the prince must have a just intention (intentio recta), which only exists when the aim of the war is to punish the wicked, to help the good and thereby to restore peace as soon as possible. The need for the war to be waged by a sovereign means primarily the strict rejection of ‘private’ wars—the feuds that neither the Peace of God nor the public peace had rooted out or even substantially limited—which were thus flatly denied the character of war, with appropriate legal consequences. On the other hand, it is clear that St Thomas understood the factual situation realistically, by acknowledging the existence of independent States side by side, ie the State system of the later Middle Ages, which was being established in the 13th century. (By contrast, his slightly older contemporary Hostiensis [Henry of Segusia] was still arguing in 1260 in favour of the idea of an Imperium Christianum uniting the whole of Christendom, and maintaining therefore that only action against non-believers should be recognized as war in the legal sense.) St Augustine also required an intentio recta, but in the developed system of St Thomas it had far-reaching consequences, one example being that a person who fights in what is in itself a just war for the sake of booty, although not guilty of robbery—that is prevented by the objective justification for the war—nevertheless commits a sin (op. cit., Quaestio 66). The idea that everything depends in the end upon the moral blamelessness of conduct, which is central to St Augustine’s thought, also dominates the scholastic system in spite of all the unavoidable concessions to the objective facts.

E.  Late Middle Ages (1300 to 1500)

52  The European State system, which had completed the initial stage of its development by about 1300, was further strengthened and consolidated in the last two centuries of the Middle Ages. Dante’s dream of a universal monarchy, which would resolve all tensions, and even further, Bartolus’ argument that the Emperor, a supreme feudal lord of Christendom, was so superior to the other Christian princes that he even had the right to forbid them to wage war, were now completely irreconcilable with reality. The autonomy of the European States and the sovereignty exercised by their rulers independently of the Emperor and the Pope, with increasing support from theorists, did not, however, mean that lesser rulers did not continue to deal with each other as sovereign powers. Nor did they prevent a confederation of cities such as the Hanseatic League—at any rate while it was at the height of its power from the middle of the 14th until towards the end of the 16th century—from dealing with foreign rulers not merely in the style of a sovereign, under the title adopted in 1358 of ‘Cities of the German Hanse’, but as a sovereign recognized in practice, making alliances, waging war and concluding peace treaties; and that took place even though its German member cities were all subject to the authority of the Emperor, and some were additionally subject to that of a territorial lord. The major part of the maritime law followed by the Hanseatic League is contained in the Maritime Code of Wisby (around 1407); its provisions relating to the law of maritime warfare (Naval Warfare) conform in many points with those of the Consolato del Mare, which was compiled in Barcelona at about the same time (Law of the Sea, History of).

53  The maintenance of peace continued to be furthered by the use of arbitration, which was now firmly established in wide areas of the law and to which even the highest ranking powers not infrequently submitted; its extensive effectiveness only came to an end as circumstances changed fundamentally at the close of the Middle Ages.

54  The maintenance of peace was also the aim of peace plans, the first of which date from this period, such as that of the French jurist Pierre Dubois, written under the title De recuperatione terrae sanctae around 1305, and that of the Bohemian King George Podebrady, dated around 1462. The desire for peace is also the principal theme of Dante’s political writings; it occurs in the work of the scholastics and in the Defensor pacis (1324) of their great rival, Marsilius of Padua. The two peace plans differed from earlier ones in that the authors were not content to express the age’s longing for peace in the traditional forms of complaint or in an honestly perceived, but unrealistic and impracticable vision of a future better world, but instead produced concrete, detailed plans for the union of the Christian States, which anticipated to an amazing extent developments which have only come about with the latest evolutions in the law of collective maintenance of peace.

55  The laws of war were dealt with by the Bolognese jurist Giovanni da Legnano in his Tractatus de bello (1360). This is noteworthy as the first comprehensive account of the subject, but it does not develop the principles substantially beyond the position established in the 13th century. By contrast, the Arbre des batailles, written around 1385 by the Augustinian Prior Honoré Bonet in southern France, marked a major advance in this area. Bonet had also studied law and followed traditional doctrines closely in the specifically legal parts of his book; but in spite of the mediaeval trappings there is a remarkably modern spirit in his rules for the conduct of warfare by knights. In a conscious return to the provisions of the Pax Dei, which the scholastics had generally passed over in silence, Bonet set human standards for the conduct of warfare. It is true that his work had no discernible influence on the practice of his own time, but the large number of manuscripts and copies testifies to the extraordinary impression which it made on his contemporaries and successors. Anyone who believes in the lasting power of formulated ideas will be in no doubt that the humanization of the customs of war which began in the 15th century was inspired at least in part by Bonet’s writing. Both Bonet and Giovanni da Legnano owe a substantial debt to the Tractatus represaliarum of 1354 by Bartolus; this work is written against the background of the new international order of the Late Middle Ages and its importance for the development of modern international law has not yet been sufficiently recognized.

56  The middle of the 15th century saw the beginning of the practice of permanent diplomatic missions, and in the early 1430s we find the first discussions of the legal requirements for the acquisition of overseas territory (Territory, Acquisition). In both cases, the law has only been fully worked out in the course of modern times, but the importance of these developments for the shaping of modern international law is evident from their beginnings.

57  The introduction of permanent diplomatic missions bears an almost revolutionary character. Until about the middle of the 15th century, rulers had only sent and received extraordinary envoys for particular cases. The Roman Republic at the height of its power and even the Byzantine Emperor were content to conduct their often extensive international dealings in this manner. The new form of diplomacy originated in Italy. Here, an unstable system of ancient principalities, new dictatorships, and oligarchically ruled city republics, all of which endeavoured to establish themselves as independent powers, emerged in the 14th and 15th centuries alongside the Pontifical State. Force was the traditional means of achieving one’s aims, but the use of force was becoming increasingly expensive and uncertain in the age of mercenary armies (Mercenaries). The Italians of the time, with their notorious military inferiority on the one hand but their superiority in bargaining on the other, were virtually forced to use primarily diplomatic means to achieve their political goals. Permanent envoys facilitated dealings with friendly governments and they frequently enjoyed the confidence of both sides. Given the difficulty of transmitting information, permanent envoys also offered the best possibility of keeping abreast of affairs in the other country. Hence they occurred, even before the middle of the century, in the relations between Milan and Florence, for example. Non-Italian States remained hesitant. We know that Louis XI of France (1461–83), the best-known politician of the age, declined either to receive or send permanent envoys; for him an envoy was still predominantly a dangerous observer, even a spy, and the sooner he left the country the better. In this instance, the system of alternating missions was retained as long as possible, and even in Italy it remained alongside that of permanent envoys for a long time. Diplomatic missions only reached the highest possible stage of their development in modern times, when the permanent representative of a foreign State enjoyed the same friendly relationship with the statesmen of the receiving State as had been characteristic of the early history of the institution.

58  Arguments over the legal basis for acquisition of territory overseas began with the peace Treaty of Medina del Campo in 1431, which sought to end several decades of succession disputes between Portugal and Castile and in which, in order to make the peace complete, the parties not only recognized each other’s existing colonial possessions but assured one another that they would respect the overseas areas of interest described in the treaty. The confirmation of the treaty by a papal edict obtained by the parties in the same year did not alter the fact that the division of the areas and the definition of interests had been made primarily by an agreement between two independent States, to which the consent of the Curia only added a kind of higher guarantee. It was a different matter when the Portuguese saw themselves compelled, after the capture of Constantinople in 1453, to find a new sea route to South-East Asia in place of the land route, which had been closed. To begin with, this route had to lie along the West African coast, in other words on a route used exclusively by Portuguese ships up to then. Here, there were no existing conflicting interests of another power with which the Portuguese would have to come to terms, but there was, of course, the possibility of some (as yet unknown) future rival, whose appearance they aimed to prevent. This was done by the Portuguese King in acknowledging the feudal lordship of the Pope in respect of all Portugal’s present and future colonial possessions: Nicholas V’s bull Romanus Pontifex of 8 January 1454 granted them this protection. This papal act did not exclude the possibility of reaching agreement with some later rival regarding overseas areas yet to be discovered, and to that extent the principle followed in 1431 was still preserved; the crucial point, however, was that now the legal title was based on enfeoffment by the Church, whose protection still worked to the advantage of the Portuguese in the Peace Treaty of Alcáçovas (1479). The legal settlement following the occupation of the West Indies by Columbus in 1492 initiated a new phase in the development of the law, which links up with the other changes occurring at the beginning of modern times.

F.  The ‘Spanish Age’ (1500 to 1648)

59  The year 1494, in which the struggle of the Western European countries for Italy began with Charles VIII’s march from France to Naples, does not mean, as was long thought, the sudden and unexpected start of a new European State system. The international order of modern times based on independent nation States (State) of equal rank had been developed in all essential aspects by the end of the 13th century. Nevertheless, the system existing in the Late Middle Ages underwent considerable change in several respects around the turn of the 15th century. One decisive factor in this was the development of the Spanish Habsburg Empire, which brought the areas of Eastern Europe into closer contact with the West—they had, up to that time, stood more or less outside the Western State community—and thereby initiated a period of immense expansion of the international legal community, which has only been completed in our own day. The menacing ascendancy of this Empire also provided the decisive stimulus for the development of the principle of the balance of power in Europe, from the idea of the weaker States joining together in a deliberate attempt to counteract the power of a strong State, a practice which first appeared in Italian diplomacy in the 15th century. The balance of power principle became the main foundation of international politics in the following centuries and has profoundly influenced modern international law. Although it was not the first time that the legal problems raised by colonial expansion (Colonialism) had arisen, nevertheless the disputes following the appropriation of the West Indies marked at any rate a relatively new stage in the development of international law, especially in view of the large number of nations in contention, the imminent modification of the legal requirements for the acquisition of overseas territory and the increasingly important problem of the treatment of the native population. Among the questions of international law which appeared for the first time in the 16th century was that of the position in international law of States which did not readopt the old faith after the Reformation. Finally, there was no parallel in previous centuries with the importance accorded to theory from the beginning of the 16th century—a consequence of the respect for learning and education characteristic of humanism and the Renaissance. Over and above this contemporary influence, however, it must not be overlooked that—by comparison with other fields of human activity—the political theory and the theory of constitutional and international law of the period has had great practical consequences for international relations in modern times. The years around 1500 can thus be seen as the beginning of a period when so many previously unknown forces were released that changed the traditional picture in important respects, that it would not be right to pass from an account of the international law of the Late Middle Ages to a discussion of the law of the modern era without marking this turning point.

60  This first period of modern international law ends with the Peace of Westphalia (1648) (Westphalia, Peace of [1648]), which established peace throughout Europe and was the most important document in European public law for centuries.

61  Grewe’s expression ‘the Spanish Age’ is the most appropriate name for an era marked by the political and, to a certain extent, intellectual supremacy of Spain. There was hardly a single important problem of international law until the middle of the 17th century that was not principally a problem for Spain and the allied Habsburg countries. The idea of the balance of power in Europe, the questions of law connected with the acquisition of colonial territories overseas, the recognition of States, the legality of intervention for religious reasons—all these questions naturally concerned the other States to a greater or lesser extent. Spain, however, was always affected, and the national ideologies which it supported were always involved, even if they did not prevail in a particular case.

62  The unusual respect enjoyed by theoretical work in all fields from the beginning of the 16th century and which far exceeded anything that had gone before, had its most far-reaching practical effects in the area of international relations. Any attempt to provide a survey of the legal features of an international nature in this period must therefore begin with the underlying theoretical doctrines.

63  At the head of the list—both in time and in the influence of his writings—stands the Florentine Niccolò Macchiavelli (1469–1527). His ideas on the State and statesmanship are recorded in memoranda and dispatches and brought together in the voluminous ‘political observations’ (Discorsi sopra la prima deca di Tito Livio, 1513–17), although when compared with the famous treatise Il Principe (1513), these observations do not deserve any special interest. What is fundamentally new in Machiavelli’s political theory is his doctrine that in the event of an otherwise irresolvable conflict between the dictates of morals or the law on the one hand and elementary interests of the maintenance of internal State power or the preservation of the State against external enemies on the other hand, a ruler may, indeed must, allow what Machiavelli’s compatriot Francesco Guicciardini later called ‘reasons of State’ to take precedence over morals and law. Moral or treaty obligations can play no part when political necessity requires one to disregard them. In this way, conduct which, although occurring countless times in practice, must always have been regarded impermissible by those resorting to it, was not merely justified in theory but indeed positively prescribed. Herein lies the real importance of Machiavelli’s theory for foreign policy and international law, and not in the practical suggestions he makes, which those concerned with the major issues of politics certainly did not need. Machiavelli’s theory provided the basis for the development of the modern State as an end in itself, a sovereign body in the most extreme sense, whose international obligations were either not regarded as legal at all or could easily be swept away in a particular case on the principle of clausula rebus sic stantibus (Treaties, Fundamental Change of Circumstances). Some considerable time had to pass, however, before the State became as free of obligation in practice as in theory, and only the beginnings of this development fall into the period under consideration.

64  A political thinker in the first half of the century and a lawyer in the second half, the Frenchman Jean Bodin (1530–96), in chapter 8 of his principal work on public law (Les six livres de la République, 1576), defined sovereignty in the following words, in the Latin version of 1586: ‘Maiestas est summa in cives ac subditos legibusque soluta potestas’ (‘the Sovereign has supreme power over citizens and subjects and is not bound by any laws’; translation by the editor). This formula subsequently became the generally accepted definition, but it gives an imperfect picture of Bodin’s views. He did indeed claim both external and internal independence for the State, but, as the context of the relevant passages shows beyond any doubt, he did not hold that the State could therefore unilaterally renounce obligations undertaken (Pacta sunt servanda). With regard to internal relationships, a general obligation on the State to perform its undertakings follows from the doctrine of social contract of which Bodin was an adherent. The binding force of international agreements, however, is derived from the principle of keeping faith with one’s agreements, which Bodin supported by detailed arguments; since all obligations are undertaken out of necessity, agreements must be observed even when made under pressure. The contrast with Machiavelli could not be starker, and it is understandable that Bodin, the lawyer, profoundly disliked the Florentine, for whom the law only existed to the extent that it could be used as a pawn in the game of politics. Nevertheless, the development of the modern concept of sovereignty originated with Bodin’s convenient formulation, and Bodin himself was regarded for much of the modern age as the founder of the doctrine of the unlimited and illimitable power of the State.

65  The Spanish late scholastic school, which flourished in the 16th century, and of which the most eminent representatives were the Dominican Francesco de Vitoria (around 1483–1546) and the Jesuit Francisco Suárez (1548–1617), further developed the teachings of the scholastics of the High and Late Middle Ages with regard to international law in general and the law of war in particular, and endeavoured with some success to master the numerous new problems arising both nationally and internationally in a manner which took account of the changed circumstances, yet basically maintained traditional legal forms.

66  Vitoria, who is so called after his Basque place of birth (the Latinized version of the name is Victoria), held for the last 20 years of his life a chair of theology at Salamanca, the country’s leading university. His views on international law are known principally through his two lectures from the years 1537–39, of which transcripts have survived, on the legal position of the natives in the recently discovered West Indies and on the laws of war applicable to them (De Indis recenter inventis and De iure belli Hispanorum in barbaros). Vitoria starts with the question, which is an obvious one for a theologian, whether children of the inhabitants of the West Indies, who came under Spanish rule in 1492, could be baptized against the wishes of their parents. To answer this question he goes back to first principles. He first asks by virtue of what law did the natives come under Spanish rule at all, then what rights the Spanish rulers or the Church had acquired over them in temporal and spiritual matters. Vitoria uses these issues as the occasion for what is in effect an outline of international law and its spiritual bases. The result was certainly not a complete and exhaustive treatment of the subject, such as that by Hugo Grotius at the beginning of the following century. Above all, it was more the work of a theologian than of a lawyer—Vitoria himself emphasizes that questions of this kind are not for the lawyer who is inexperienced in the ius divinum, but for the priest who deals with matters of conscience. It is, however, a well-rounded treatment, inspired by practice and intended for practice, of basic problems of international law of a kind unknown until then.

67  Vitoria had to consider the following factual and legal problems: as Spain set about taking possession of the newly discovered areas after Columbus’ first voyage, Portugal objected, relying on the monopoly granted to it by the Pope in 1454. The two States entered into negotiation[s] with each other and with the Curia, which were protracted but which finally led to a compromise. Through Alexander VI’s edict Inter cetera, retrospectively dated 4 May 1493 (when the negotiations commenced), and a supplementary edict, retrospectively dated 26 September 1493, all land areas and islands, whether discovered or to be discovered, 100 miles (according to the measurement of that time approximately 550 km) west of the Azores and the Cape Verde Islands, were awarded to Spain under the legal form of a mandate (Mandates) with the sole duty of performing missionary activities (Missionaries). By the treaty of Tordesillas of 7 June 1494, concluded by Spain and Portugal without papal involvement, the demarcation line was moved 270 miles further west in Portugal’s favour. This change in the line did not alter the fact that the entire New World was divided into fiefs of the two Iberian nations.

68  The Spanish colonial administration based the discharge of its missionary responsibilities on the much quoted sentence in the edict of May 1493: ‘barbaricai nationes deprimantur et ad fidem ipsam reducantur’. The native population was treated, without any misgivings, as completely devoid of rights, since they were heathens and consequently in a state of mortal sin, and the administration claimed exclusive power to deal with the natives’ liberty, faith and property. This ‘conquistador ideology’, as propounded by Sepúlveda and other lawyers at the royal court, had been objected to by notable representatives of the ‘missionary party’ decades before Vitoria appeared. His legal and theological arguments on the question of the natives were therefore, for the major part, not new. The objection, in particular, that the Pope was no more ruler of the world and entitled to divide it up than the Emperor, which had been one of the principal arguments in the Late Middle Ages in the struggle against the Western universal powers, had been repeatedly advanced in the debates on the treatment of the natives. This does not, however, detract from the merit of Vitoria’s work. His particular achievement, which brought him great fame in his lifetime and finally even the recognition of his opponents, does not lie so much in his production of new legal arguments, as in the logical clarity with which he develops the arguments, his sure eye for what is essential and effective, his courageous honesty in making his views known, even when they ran counter to the official teaching of the time, and finally in the humanity which governs his arguments in spite of his efforts to present them with legally compelling logic.

69  The theory of the laws of war was developed in the first half of the 16th century in a manner which had fundamental importance for the future. As early as 1512, Matías de Paz, a professor in Valladolid, argued in his treaties De dominio regum Hispaniae super Indos that a war with those who were to be converted could be a just war for both sides: for the Spanish, because they were fighting for Christ, and for the barbarians because they were defending their country without knowing the Holy Name ‘for sake of which war was being waged against them’. This concept of a bellum iustum ex utraque parte was taken up and generalized by Vitoria: if the opponent of a party waging a just war is in a state of invincible error (error invincibilis) concerning his own justification for waging war, so that there is no fault on his part, a justified ‘punitive’ war against him is not possible and the war can, in this case, only serve the purpose of restoring the law. This meant, however, that in practice the doctrine of the just war had been abandoned, at least in its traditional form, based on the drawing of a clear distinction between objective right and wrong, and that unintentionally but inevitably, the first step had been taken in the direction of the modern concept of neutrality by choice and the unfettered right of sovereigns to wage war.

70  The most important representative of the Spanish late scholastic school besides Vitoria was Francisco Suárez, most of whose numerous writings are devoted to religious subjects. In the legal field, he was interested principally in problems of natural law and national law. He also made contributions to the study of international law, however, the lasting effect of which was guaranteed by his worldwide reputation in the 17th century. Although Suárez, too, did not define the term ius gentium to cover exclusively international law, he succeeded in separating international law from natural law within ius gentium. It is not the content but the normative force of international law which is derived from natural law. The natural law principle of keeping faith with one’s agreements, which has no substantive content of its own, enables legally binding rules of international law to be created. With regard to the concept of sovereignty, Suárez too did not escape the influence of Bodin’s formulation, but when he taught that the State was only supremum in sio ordine because the rights of sovereignty had been given to it by the superior order of international law, he was raising an objection to the very origin of consent theory, regardless of the form it might take, an objection which has proved to be irrefutable in principle, and the basic idea of which survives in the modern view of the binding force of rules of international law.

71  The State system of the Spanish Age comprised basically all the Christian nations of the West, as in the Late Middle Ages. However, in spite of the continuing nominal equation of the international legal community with Christendom, the medieval unity was irretrievably lost after the Reformation. The struggle of the Protestant States, which lasted more than a hundred years until the Peace of Westphalia, to obtain unrestricted legal recognition for themselves and the denial of the legality of intervention on religious grounds, forms a kind of dismal constant in a period otherwise largely lacking in uniformity (Intervention, Prohibition of). On the other hand, the alliance concluded by Francis I of France in 1535 with the Porte, the first ‘capitulation’ of a Christian State with the new leader of Islam, did not have the exceptional character which has been claimed for it. There had always been legal ties between Christian and Mohammedan States and even impia foedera were concluded throughout practically the whole of the Middle Ages, notwithstanding the religious prohibitions on both sides. Nevertheless, the political significance of the event was indeed extraordinary: the treaty brought the French that increase in political standing which they needed in order to hold their own against the superior might of the combined power of the Habsburgs—an early and important example of a deliberately pursued balance of power policy. (Francis I told the Venetian ambassador: ‘The Turks…give the Emperor trouble and thereby increase the security of other potentates’.) At the same time, it obtained an advantage for them in the whole Levant, which others could not make good until the 19th century.

72  The development of the modern State continued in this period. The State was still, for practical purposes, the sole subject of international law, with the notable exception of the Order of Malta, which remained a recognized member of the international legal community, in spite of the loss of its territorial base in 1522 (Malta, Order of). Nevertheless, the State did not attain the condition of complete ‘impermeability’ in all areas, in particular in that of territorial sovereignty, which have become characteristic of the State in more recent times. It must also be borne in mind in relation to all the constitutional and international law of the period that we were not yet dealing with the ‘fully developed form of the modern State which exists independently of those who wield power in it’ (Grewe 46); commitments undertaken were still closely linked with the person of the sovereign, and treaty obligations prima facie lapsed at his or her death.

73  The connected question of the conditions on which a new de facto independent State could claim to be recognized as such and thus admitted to the international legal community was raised in this period by the case of the Netherlands. For Spain, Baltazar Ayala (1582) argued that subjects had no right to rise against their prince in any circumstances and that only the Pope had the right to remove a tyrannical ruler. Subsequent events took away the foundation of this argument that was based on the curialistic doctrines of the Late Middle Ages; Spain found itself compelled to agree to several long-term armistices with the rebels, whom it was unable to defeat, and in the Peace of 1648 finally had to recognize the breakaway provinces as a free and independent republic. This opened the way for the development of the modern principle of the recognition of States, which does not examine the legitimacy of a State’s origin, but requires only the presence of the factual requirements for a viable State.

74  The division of the New World by papal edict had brought immediate protests from the nations who were excluded from it. Admittedly it proved impossible to counter the Spanish-Portuguese expansion with anything other than words until the last third of the 16th century. English and Dutch sea power were only in the early stages of development, and France was not in a position to break the Iberian States’ de facto colonial monopoly on its own. The fact that the latter no longer sought papal authority when defining their Pacific interests in the Treaty of Zaragoza (1529), and increasingly based their further overseas expansion on the then almost generally accepted principle of acquisition of title by right of first discovery (Territory, Discovery), can be regarded as one of the first successes for the rival nations. When the battle for the colonial territories reached its full intensity, as English and Dutch power increased towards the end of the century, attempts were made to preserve the balance of power, and with it peace, in Europe by agreeing on certain demarcation lines in the oceans (lignes des amitiés et des alliances; ‘lines of amity’) beyond which the European state of peace did not apply. This strange division of the world into one area in which might was right and another area of peace unaffected by events in the former, occurs in treaties made by the colonial powers until the early decades of the 17th century. It was not until the Madrid peace treaty in 1630 that England and Spain agreed that peace should also extend to those areas which lay ‘beyond the line’; by then the world had become too small for peace to be divisible.

75  Closely connected with the question of colonial expansion and its legal basis was the problem of the freedom of the seas. Grotius’ well-known polemic Mare liberum, which was published in 1609 (and in substance reproduces chapter 12 of his work on the law of prize, De iure praedae, completed in 1606, but not printed at the time and rediscovered in 1868), claimed unrestricted access to the East Indies for Dutch merchant ships. It was written at a time when Grotius was in the service of the Dutch East India Company (founded in 1602), one of those large, privileged trading companies to which powers of government were entrusted (governments). Such trading companies, established principally in England, the Netherlands, and France in the first half of the 17th century in accordance with the new mercantilist economic theories, but reaching the height of their powers in the later 17th century and in the 18th century, are best dealt with in the context of the succeeding period of the history of the law of nations.

76  Mare liberum was aimed at Spain, which had acquired Portugal’s colonial possessions on the latter’s defeat in 1580. The reply came from England, however, in the form of John Selden’s work on the ‘closed sea’ (Mare clausum seu de dominio maris), which was commissioned by the Crown and completed in 1618, but not published until 1635. The dispute between Britain and the Netherlands, which lasted until after the end of the present period, concerned the question of the recognition of an oceanus britannicus and the limits of coastal waters; the common struggle against Spain with regard to shipping on the high seas was unaffected by it.

77  The practice of permanent diplomatic missions made only slow progress north of the Alps in this period. The strength of the resistance to it in the 17th century is shown by the much quoted passage in which Grotius dismisses it as superfluous (De iure belli ac pacis book II ch 18 section 3). A long time was needed in these circumstances before an envoy became a welcome guest, instead of a suspected spy, and a respected representative of a State of equal standing instead of a mere supplicant. The Peace of Westphalia of 1648 also brought this stage of the development of the institution to a close.

78  The highly developed system of international arbitration in the Middle Ages could not maintain its position with the rise of the absolute State opposed to any superior power, and it was reduced almost to insignificance. Theoretical interest in the institution increased, however, as its use in practice declined. The two great peace proposals of this age were that of the French scholar Eméric Crucé (Le Nouveau Cynée, published in 1623), and the European plan of Henry IV of France’s leading minister, the Duc de Sully; the latter plan, inspired by the ideas of Henry IV and developed in the decades after the King’s death in 1610, appeared as the 30th book of Sully’s memoirs, completed in 1638. The two proposals agreed in providing for the establishment of councils based on the principle of equal representation, having, in addition to their political functions, the role of permanent courts of arbitration with compulsory jurisdiction. It is characteristic of Sully’s approach, with his practical experience in politics, that he considered that a real balance of power must first be established as the basis of all efforts to maintain peace. Crucé, for his part, was far ahead of his time in calling for decisions by majority vote, peaceful settlement of international disputes and the application of moral, and if necessary military, force in the enforcement of collective decisions. Other peace plans of such a detailed nature were not, however, produced during this period. The desire for a peaceful world found expression in other ways; in many of Erasmus of Rotterdam’s writings on peace, of which his Querela pacis (‘Plea for Peace’, around 1518) is the best known; in the works of Jean Bodin, whose Colloquium heptaplomeres (discovered only in the 19th century) is a call for religious tolerance; and in the Civitas solis (‘The Sun State’) and other works of Thomas Campanella, who continued to see the salvation of Christendom in a hierocratic world government headed by the Pope.

79  The development of the doctrine of bellum iustum into that of war that could conceivably be just on both sides, a development associated with Vitoria, provided the theoretical basis for the development of the modern concept of neutrality. The requirements and substance of neutrality were only fully developed after the middle of the 17th century; Grotius (De iure belli ac pacis book III ch 17 section 3) still held the granting of rights of passage and the provision of supplies to belligerent armies to be consistent with neutrality, as long as both sides were treated equally (Belligerency). To what extent actual practice complied with the increasingly insistent demands of contemporary theory for the humanization of warfare is difficult to judge; there are examples of correct, decidedly humane behaviour, but there are also more than a few instances of conduct as brutal as before. An institution, which seems surprising now but which had existed in a similar form in the international law of the Middle Ages and in that of Ancient Greece and that had survived down to the 18th century, was that form of authorized self-help known as ‘special reprisals’. If a subject who had suffered unlawful damage at the hands of subjects of another State and had been refused redress obtained a ‘letter of reprisals’ from his ruler, he was entitled to take action against compatriots of those responsible to make good the damage. It is quite possible that this sort of private warfare, by confining the consequences of the dispute to a limited circle of persons, prevented the outbreak of a full scale conflict in one case or another.

80  The beginning of the Spanish Age was marked by an immense increase in concern for theory, and towards its end it produced a man who brought together the whole of the theory and no small part of the practice of international law at that time in a single major work. That man was the Dutchman Hugo Grotius (the Latin version of de Groot), who was born on 15 April 1583 in Delft and died at Rostock on 28 August 1645, after being shipwrecked in the Baltic. He has already been mentioned as author of the polemic on the freedom of the seas, as well as with regard to his views on the introduction of permanent diplomatic missions and the problem of neutrality. His real achievement for international law did not lie so much in the discussion of particular problems but in his mastery of the subject as a whole, demonstrated in his principal work De iure belli ac pacis libri tres (1625; four further editions appeared in his lifetime). The great advance over previous writings is the separation of international law from other areas of law and its development as an area of law in its own right; this is found for the first time in Grotius, and provides ample justification for regarding him as the real founder of an independent science of international law and therefore as the ‘father of international law’.

81  This view does not underestimate the importance of his predecessors. How much Grotius owes to the Spanish late scholastic school, and in particular to its first great representative, Vitoria, is obvious. Of the writers who influenced Grotius, the Italian Alberico Gentili (1552–1608) should also not be forgotten. Gentili emigrated to England because of his religious beliefs and eventually became a professor at Oxford. He was the author of the earliest treatise on the law of diplomatic missions (De legationibus libri tres, 1585), which grew out of a legal opinion and adopted a historical approach, and a treatise on the laws of war (De iure belli libri tres, 1598) based on positive law. None of this diminishes Grotius’ enormous original achievement in any way. Notwithstanding all the weaknesses and shortcomings in detail, his work has, for centuries, been the primary textbook of international law for practitioners, scholars and for others interested in the subject—the work by which they have been guided and with which they started, even if in the end they reached different conclusions. This truly enormous influence does not primarily rest, however, on the impressive fullness of the material dealt with, nor in the polished style, but on Grotius’ absolute belief in the law, which fills the entire work and gives the reader the strong impression that here ‘the law is really being taken seriously’ (Wolf 287).

82  The end of the period is marked by the Peace of Westphalia of 1648, a settlement of equal importance in the contexts of politics, constitutional law and international law. As with all epoch-making events, one can argue whether the Peace of Westphalia was the conclusion and summation of what had gone before or the beginning of something new. There are good arguments for both views. In relation to international law, however, the main weight must be given to the new order that it created and to its effect on the future. In defining the scope and structure of the Roman Empire and its members, and introducing the principles of religious equality and the equality of diverse States into the practice of international law, so many essential features of the modern State system were established as a result that the Peace of Westphalia can justifiably be regarded as a kind of European ‘Basic Law’, which remained in force up to and beyond the French Revolution. Its consideration, therefore, belongs not at the end of the present section but at the start of the new period which commences with it.

Select Bibliography

Pre-Classical Antiquity:

Ancient Greece and Persia:

Romano-Hellenistic Period:

Transition from Antiquity to Middle Ages (AD 400–800):

Early and High Middle Ages (800 to 1300):

Late Middle Ages (1300 to 1500):

The ‘Spanish Age’ (1500 to 1648):