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I Actors, 3 Peace Treaties and the Formation of International Law

Randall Lesaffer

From: The Oxford Handbook of the History of International Law

Edited By: Bardo Fassbender, Anne Peters

From: Oxford Public International Law (http://opil.ouplaw.com). (c) Oxford University Press, 2015. All Rights Reserved. Subscriber: null; date: 27 September 2020

Peace treaties — Treaties, ratification — World War I to World War II — Peace keeping

(p. 71) Peace Treaties and the Formation of International Law

1.  Introduction

Ever since pre-classical antiquity, peace treaties have been important instruments for ending wars as well as for the political and legal organization of international communities. Peace treaties were of particular importance to Europe and the West between 1500 and 1920. The relative number of wars which were ended through peace treaties steadily rose from less than half in the 16th century to almost 90 per cent at the beginning of the 20th century.1 Peace treaties played a primary role in the formation of Europe's classical law of nations (1500–1815) and the West's modern international law (1815–1920). Historians have long since acknowledged that the string of peace treaties that runs from Westphalia (1648) to Versailles (1919) formed the backbone of Europe's international constitution. These and other peace treaties laid down some foundational principles of international order, such as religious neutrality, the common responsibility of states for upholding peace and stability, the special role of (p. 72) great powers therein and the balance of power.2 But peace treaties are also an informative and constitutive source of two essential, specific branches of international law, the law of treaties and the ius post bellum. To these two aspects of the contribution peace treaties made to international law, scholars have devoted far less attention than they deserve. Particularly the latter is of great importance for the study of international law and for understanding its impact on people's lives. The ius post bellum forms the third logical part, next to the ius ad bellum (use of force law) and the ius in bello (the laws of war) of what was historically known as the ius belli ac pacis (laws of war and peace).3 Between the 16th and the 20th centuries, a large body of law on the ending of war and the restoration of peace was articulated in peace treaties.

2.  Classical and Medieval Peace Treaties

The Roman usage and customs of peace treaty-making were informed by Greek practices, which in turn drew on those of the pre-classical civilizations of the Middle East. By consequence, ancient peace treaty practice shows a remarkable continuity.4

All through antiquity, peace treaties were primarily oral agreements. The constitutive element of their binding character was the mutual oath undertaken by treaty partners. Typically, the oath would include an invocation to the gods to act as witnesses and guarantors of the treaty. Already in pre-classical times, there are examples of treaties negotiated by ambassadors, which were later ratified by oath by the rulers. The Romans distinguished between foedera and sponsiones. A foedus was the traditional form of a treaty whereby the Roman people bound themselves. Initially, it was sworn to by fetial priests through an elaborate ritual, committing Jupiter, the supreme deity, to the treaty. The fetials would only act after a positive decision of the Senate. Later, they were replaced by magistrates, and ultimately by the emperor. A sponsio was an agreement entered into by Roman magistrates, often commanders in the field, at their own initiative. It had to be ratified by the Senate and people of Rome. The (p. 73) Romans reserved the right not to ratify these engagements, under the condition that they surrendered the magistrate who made the sponsio. In antiquity, peace treaties were commonly written down and published on pillars or tablets. Its recording was not constitutive to the treaty but served as proof for the treaty text and was a way of making it known. The Greeks, and through their influence, the Romans, also developed the concept of faith (πίστίς‎, fides) to the given word as a foundation for the binding character and the strict upholding of a treaty.

Ancient peoples distinguished between peace treaties and armistices. Greek peace treaties were almost always made for a limited time. The Romans reserved the term pax (peace) for the state of peace, to be distinguished from the state of war. The peace treaty itself they would refer to as foedus pacis.5 Indutiae was the term used for armistices. Until the early 3rd century BC, the Romans would use indutiae for peace treaties limited in time, which restored the state of peace for a long period. After that, the term indutiae gained its meaning as a treaty suspending hostilities but not ending the state of war or restoring the state of peace.6 The glossator Accursius († 1263) distinguished between indutiae, armistices only suspending hostilities during war, and treugae, truces temporarily ending war and temporarily restoring peace.7

Ancient peace treaties were brief and, with the Greeks and the Roman, clauses were standardized. In ancient peace treaties, the three main categories of clauses that could later be found in (early-)modern peace treaties can already be distinguished: first, clauses dealing with the issues underlying the war; second, clauses ending the state of war, thus reflecting upon the past; and third, clauses restoring and safeguarding the state of peace, thus referring to the future. Just like early-modern peace treaties, ancient peace treaties often included stipulations on prisoners of war. In this context, the Roman ius postliminii should be mentioned. The ius postliminii implied that Roman citizens, who were taken captive by the enemy and lost their citizenship and all their property, regained their rights upon their return. The Greeks introduced general peace treaties, which did not only involve the actual belligerents but extended to third powers. These treaties included the provision that all powers involved would commonly act against the perpetrator of a breach of treaty.

The Roman practices of peacemaking did not disappear with the fall of the Roman Empire in the West (476 ad). They lived on through the early Middle Ages, in the practices of the Byzantine Empire, the Germanic successor kingdoms, and the Islamic (p. 74) world.8 All through the Middle Ages, ratification by oath remained the foundational stone of the binding character of treaties. In the Latin West, oaths were taken in church whereby the Holy Gospel, the Holy Cross, the Eucharist, or relics were touched. Under canon law, the enforcement of treaties fell under the jurisdiction of ecclesiastical courts, as the breaking of a promise was a sin. This was all the more true for treaties confirmed by oath, as perjury was considered an even more grave sin.9 In the 15th and 16th centuries, princes would often expressly subject themselves to ecclesiastical or papal jurisdiction and sanctions, up to excommunication.10 In some peace treaties, princes renounced the possibility of denouncing their oath as invalid and requesting the pope for dispensation from their oath.11

The learned ius commune of Roman and canon law contributed to the development of a doctrine of peacemaking from the late 11th century onwards. The laws of war and peace did not form an autonomous body of law with its own literature. Roman and canon lawyers would comment upon issues relating to war and peace at appropriate places in their general writings. Only in the 14th and 15th centuries, self-standing treatises on matters of war and peace would appear. Treatises on peace treaties were few and far in between.12 Justinian's (527–65) collection of Roman law held scant evidence of Roman peace treaty practice. Most relevant was title D. 49.15 De captivis et postliminio et redemptis ab hostibus from the Digest which informed about the distinction between foedera and indutiae and about postliminium. Therefore, Roman jurisprudence could add little knowledge to what had remained from Roman peace treaty practice all over the Middle Ages, but the inclusion of this information in the Digest allowed the civilians to elaborate on these subjects. The presence of the Pax Constantiae of 1183, a treaty between Emperor Frederick I Barbarossa (1158–91) and the Lombard League, in the medieval collection of the Justinian codification spurred off some writings on peace treaties.13 But by far the most significant contribution of the medieval civilians to the development of a doctrine of the law of peacemaking came through the application of Roman private law to peace treaties. To the medieval mind, this was not a ‘transplant’ but a self-evident application of the law at (p. 75) large on what was just another category of contracts. During the Middle Ages, sovereignty—superiorem non recognoscens or the non-recognition of a superior—was a relative concept and extended to a variety of rulers and communities including kings, feudal lords, and vassals, clerical institutions, towns, and even rural communities. The right to use force and make peace was not restricted to supreme princes such as the pope, emperor, or kings. Consequently, there was no strict distinction between public and private peacemaking. Among the contributions of medieval civilian doctrine to (peace) treaty making should be mentioned the use of the Roman contract of mandatum in the context of diplomatic practice.14 The contribution of canon law to the development of a doctrine of peacemaking was if anything more significant than that of Roman law. From late antiquity onwards, the Church had deferred to Roman law for its own legal organization. Isidorus’ definition of ius gentium (law of nations) with its reference to foedera pacis and indutiae had found its way into Gratian's Decretum (c 1140) and thus into classical canon law. The Liber Extra (1234) contained a title De treuga et pace,15 inducing canon lawyers to write commentaries and later, in the 15th and 16th centuries, treatises on the subject.16 The reference to ‘truce and peace’ actually stemmed from the Church's attempts from the 10th and 11th centuries to limit violence through the protection of certain persons and places (pax Dei), and the prohibition to fight at certain times (treuga Dei). Undoubtedly the most crucial contribution of medieval canon law to the doctrine of treaty law in general and peace treaty making in particular is the articulation of the principle pacta sunt servanda, of the binding character of all contracts and pacts.17 Another significant contribution from canon law and late-medieval theology is the doctrine of clausula rebus sic stantibus. The Middle Ages saw the emergence of what has been the normal method of the negotiation of peace treaties ever since. Under this method, three different sets of documents were produced: the mandates which rulers bestowed upon the representatives who negotiated with their counterparts; the treaty text as arrested by these representatives; documents attesting the ratification by oath by the rulers themselves. During the late Middle Ages, these documents were commonly made by public notaries and were signed and sealed. It was also common for the diplomats to swear an oath to the treaty text, engaging their principals to ratify the treaty with their own, subsequent oath. By the 13th century, the ratification documents came to serve two purposes. They rendered proof of the actual oath taking by the ruler, which remained the main constitutive underpinning of the treaty, making it binding and enforceable (p. 76) under canon law. But the signing and sealing of the documents had also become a constitutive act, binding the signatories under the law in general.18

3.  Peacemaking from 1500 to 1920

Between the 15th and the 18th centuries, peace treaties grew into far more extensive documents than they were before, containing a manifold of legal stipulations relating to the ending of war and the restoration of peace. This change was consequential to a change in the realities and concept of war after 1500. The rise of the modern State and the gradual monopolization of war by sovereign rulers transformed wars from a contest between princes and their allies and adherents to an all-out war between territorial States, making them more encompassing and more disruptive of normal relations between rulers and their respective subjects. This change of the reality of war was mirrored in doctrine. Under the medieval just war theory, war was perceived as an instrument of justice. It was the forcible self-help of a wronged party against the perpetrator of a prior injury. As such, the war was limited in its scope and goals to retribution for the wrong committed and compensation for the costs and damages of the war. It was also perceived as a set of separate acts of war rather than an all-encompassing state.19 Whereas the medieval concept of just war proved resilient, the 16th and 17th centuries saw the rise of a second concept of war: that of legal war (bellum legale) or formal war (bellum solemne). The concept, which was clearly spelled out by 16th- and early 17th-century writers such as Baltasar de Ayala (1548–84), Alberico Gentili (1552–1608), and Hugo Grotius (1583–1645), had antecedents in medieval civilian jurisprudence.20 For a war to be legal, it had to be waged by a sovereign and to be formally (p. 77) declared. In the latter condition lay the ratio existendi of the concept. From the 16th century onwards, formal declarations of war grew into substantial documents. The declaration of war indicated that from now on a legal state of war reigned between the belligerents and their subjects.21 By consequence, the laws of peace were superseded by the laws of war. Often, the declarations spelled out the consequences of the state of war, announcing a series of measures such as the arrest or eviction of enemy subjects, the confiscation of their property, the prohibition to pay debts to enemy subjects or their confiscation, the prohibition of trade with the enemy and of travel towards enemy territory, the eviction of diplomats, and the revocation of passports. By consequence, peace treaties had to include elaborate regulations to end the state of war and restore the state of peace.22 As declarations of war marked the beginning of the legal state of war and regulated the consequences thereof, peace treaties marked the beginning of the state of peace and regulated the consequences thereof. Early-modern and modern peace treaties had a similar structure as treaties had held before. First, there was a preamble, in which reference was made to past events and in which the treaty partners expressed their desire to restore peace and stated their main goals in doing so. Second came the material clauses and stipulations. As mentioned before, these can be classified under three headings: clauses dealing with the outstanding issues between the parties, clauses making an end to the state of war and dealing with its consequences, and clauses which pertained to the restoration and safeguarding of the state of peace for the future. Third, the treaty ended with stipulations about ratification and publication. Regarding the state of war, peace treaties would commonly have a general clause about the ending of hostilities, an amnesty clause, and include stipulations about the withdrawal of troops, occupied territory and fortresses, confiscated and sequestered enemy property and assets, pre-war debts, and wartime procedures between enemy subjects, prisoners of war, general and particular reprisals, seized documents. Regarding the state of peace, peace treaties would have a general clause about the restoration of peace and friendship, including the prohibition to harm one another or condone one's subjects to do so, and would further entail stipulations on free movement of persons, commerce, navigation, the rights of people living in ceded territories, access to justice, and protection against arrest and confiscation in case of new war. There was another reason why it was necessary to articulate the legal implications of war and peace in detail in declarations of war and peace treaties. The 16th and early (p. 78) 17th centuries were marked by a crisis of the international order of Europe. The Reformation and the emergence of the sovereign State destroyed the religious unity of the Latin West and struck hard at the last remnants of the universal authority of the emperor and the pope. The Reformation caused half of Europe to reject the authority of canon law and the jurisdiction of pope and Church. Where canon law once had been the foundational stone of the legal unity of the West and the authority on which the ius gentium rested, it now became a cause of contention. Moreover, the rise of the sovereign states devalued the role of Roman law as a common source of authority for international relations. By the mid-16th century, the authority on which the medieval ius gentium as part of the ius commune rested had collapsed. The kings and princes of Europe, who had achieved complete external sovereignty, were thrown upon their own devices, and their mutual agreements, to organize their relations. Nevertheless, many of the concepts and rules that came out of medieval jurisprudence were sustained in early-modern treaty practice and recycled—often through the mediating role of natural law—in early-modern doctrine. During the later 18th and 19th centuries, peace treaties became less extensive again. For this, several explanations can be forwarded. First, common clauses were standardized, simplified, and abridged. Second, over the 17th and 18th centuries, new or renewed general laws about the state of war and of peace were developed under the newly emerging law of nations, both in practice and doctrine. As a consequence, it became less necessary to spell them out in particular treaties. Moreover, for some clauses—such as the amnesty clause—it became generally accepted that it was automatically implied. Third, important aspects of the peaceful relations between States became the subject of separate treaties. From the late 17th century onwards, a separate treaty of friendship, commerce, and navigation was often made. In the 18th and particularly the 19th century, it became common to revive pre-war treaties on trade, navigation, and other aspects of peaceful relations which had been abrogated by the state of war, instead of negotiating new settlements in or outside the peace treaty.23 From the mid-19th century onwards, large tracks of general international law were codified in multilateral conventions. In this, the peace treaties ending the Napoleon Wars acted as trailblazers. The Congress of Vienna (14–1815) introduced or codified general international law regarding the slave trade, the status of international rivers, and diplomats. Later, peace treaties were only rarely used in this way for the formation or codification of general international law outside the ius post bellum. However, the inclusion into the Versailles Peace Treaty24 and the other Parisian Peace Treaties at the end of the First World War (1919/20) of the Covenant of the League of Nations, which among others laid out a new ius ad bellum, should be mentioned.

(p. 79) Early-modern peace treaty practice built on the inheritance of classical antiquity and the Middle Ages. Renaissance humanism (15th–17th centuries) enhanced knowledge about Biblical, Greek, and particular Roman practice through the humanists’ study of ancient historical (for example, Livy) and rhetorical texts (for example, Cicero).25 But the significance of this humanist rediscovery of Antiquity should not be overstated and certainly does not compare with the mediating role of late-medieval civilian and canon jurisprudence in the formation of the law of nations in general and the law of peacemaking in particular. The writers of the law of nations of the humanist period used ancient practices as exempla to illustrate their opinions rather than that those had a fundamental role in the formation thereof.

Between the 16th and the 18th centuries, the law of peacemaking through treaties found its place in doctrinal writings. The number of self-standing treatises on peace treaties remained very limited.26 Many of the general treatises on the laws of war and peace, such as those of Gentili and Grotius, or the law of nations (and of nature) of the 16th to 18th centuries contained reflections on peacemaking and peace treaties. In general, these were not all that elaborate or systematic. Until the 17th century, many of the old topical issues which had dominated civilian and canon doctrine were still discussed, often beyond the point of their being relevant for contemporary practice. For the writers of the 17th and 18th centuries, it can be said that, with the exception of some doctrinal discussions such as the one on the exception of duress in case of peace treaties and the clausula rebus sic stantibus, doctrine was reflective of rather than constitutive for peace treaty practice. Among the classics of international law, the treatment of the law of peace treaties by Gentili as well as Christian Wolff (1679–1754) and Emer de Vattel (1714–67) stands out for length, depth, and systematization.27 With Wolff and Vattel, the doctrine of peace treaties had been largely laid out and relatively little was added during the 19th century.28

(p. 80) The main source of peace treaties were peace treaties themselves. Diplomats and jurists based themselves on previous peace treaties and copied many of the clauses found therein. Peace treaties themselves formed the usus and rendered proof of the opinio iuris of the customary body of ius post bellum that emerged after 1500. One can distinguish several traditions of peace treaty practice according to the powers involved. Two traditions from before 1500 are foundational to subsequent peace treaty practice: the Italian practice and the practices of France, England, and the Burgundian Netherlands. Through their wars in Italy after 1494 and through the personal union between the Burgundian Netherlands and Spain under the Habsburgs (1516), the two leading powers of the 16th century, France and Spain, fell heir to these traditions. The major peace treaties of the 16th century between these powers—Madrid (1526), Cambrai (1529), Crépy (1544), Câteau-Cambrésis (1559), and Vervins (1598)—further developed the laws and customs of peace treaties and laid the basis for the general European practice of later times. To these need to be added the contribution from treaties involving England and the Republic to matters of navigation and trade and as well as that from the treaties of the Eighty Years War (1567–1648) between Spain and the Republic—in particular the Twelve Years Truce of 9 April 1609, and the Peace Treaty of Münster of 30 January 164829 that was largely copied from the Truce—to matters of private property. The peace treaties that came out of the general peace conferences of the 17th and 18th centuries—Westphalia (1648),30 Nijmegen (1678/79),31 Ryswick (1697),32 Utrecht/Rastatt (1713/14),33 Aix-la-Chapelle (1748),34 Paris/Hubertusburg (1763)35—drew on these traditions and developed the general law and lore of European peacemaking.36

(p. 81) 4.  Parties, Forms, and Safeguards

4.1.  Treaty Parties

The emergence of the sovereign State after 1500 had a deep impact on peace treaties. By the 17th century, in all major States, the right to make war and peace had become the monopoly of the sovereign to the exclusion of all subject powers, the exceptions being the Estates of the German Empire and the Northern Italian States, which fell under the feudal suzerainty of the emperor. For the late 15th century, some examples can be quoted of peace treaties between French kings and their rebellious subjects.37 But the peace agreements made between the French kings and their subjects in the context of the French Wars of Religion (1562–98) were styled as unilateral concessions by the king and were laid down in the form of royal edicts.38 After that, no regular peace treaties between princes and rebels can be found, except those ending in the successful secession of the rebels.

From the Middle Ages to the early 20th century, the preambles of the peace treaties mentioned the princes and not their realms as contracting parties. The main articles in which the state of peace was restored stated that the peace would apply between the princes, their heirs and successors, lands and subjects.39 Until deep into the 18th century, princes were mentioned by name and title; afterwards by title only.40 This was to some extent even paralleled in the case of Republics. The peace treaties entered by the Republic of the United Provinces mentioned the Estates-General, the highest sovereign body, as treaty partner and not the Republic itself.41 This would only change with the French Revolution (1789–99).42 Under this remarkable stability of form lurked an important change. After 1500, peace treaties gradually transformed from compacts between princes to public treaties between States. At the end of the 15th century, peace treaties were still personal contracts which princes made in their own name. It was the princes, and not their realms or subjects, who were bound to the treaties. The latter were only indirectly bound through the mediation of their prince and his promise to impose the treaty upon them. As princes claimed the monopoly of war (p. 82) and peace and of representing their realms on the international scene, they started to act as representatives of their realms, making their commitment sufficient to bind their realms and subjects directly. By the mid-17th century, this transformation was already well under way; peace treaty practice made this apparent in several ways. First, there was a subtle if significant change in the preambles. Until the end of the 15th century, the preambles of peace treaties expressly stated that princes entered the compact ‘for’ themselves, their vassals, and subjects.43 After 1500, these wordings disappeared and vassals and subjects were not mentioned anymore. This indicated that it was more readily accepted that the partaking of the prince to the treaty implied the allegiance of his subjects. Second, there is the question whether peace treaties were binding upon the successors of the signatories. It was generally accepted that a prince ‘could’ bind his successors to a treaty, but it was not evidently implied that they did so. Some 15th- and 16th-century peace treaties stipulated that they would remain valid for a certain period of time after the death of one of the signatories, during which his successor could ratify the treaty.44 These clauses disappeared by the 1530s. Others prescribed that the heir to the throne would co-ratify the treaty. This was largely restricted to treaties involving the cession of territories or rights.45 Third, there was co-ratification. In treaties from the 14th to the mid-16th century, it was customary for treaty partners to agree that the peace treaty would be co-ratified by certain nobles, clerics, and towns subject to the signatory princes. This had a double function: it bound the notables more directly to the treaty; often, they also promised to act as guarantors for the execution of the treaty by their prince.46 Over the 16th century, these clauses disappeared. In a limited number of peace treaties, they were first accompanied and later substituted by the promise to have the treaties registered by the highest courts, the exchequers or, exceptionally, the Estates, of the realm.47 This started as a form of institutionalized co-ratification, strengthening the allegiance of the realm to the treaty beyond the mere engagement of the prince. Although these clauses have certainly acted as precedents to constitutional rules on the ratification of treaties by legislative assemblies which appeared at the end of the 18th century, they are also fundamentally (p. 83) different. Whereas modern ratification by parliaments is an institution of national constitutional law, the early-modern involvement of representative and judicial organs was a matter of treaty law to strengthen the direct binding of a prince's subjects to a treaty. The introduction of parliamentary ratification moreover marked a final step in the transformation of treaties from compacts between princes to treaties between States.

4.2.  Forms, Ratification and Safeguards

The Reformation did not put an end to the ratification of treaties by oath. Until deep into the 17th century, the custom persisted. The Reformation, however, wrought an important change. By 1550, express references to jurisdiction and sanctions had disappeared from peace treaties, even among Catholics. The Reformation destroyed the common authority under the binding character of treaties—that of canon law. The law of nations that began to emerge as an autonomous body of law had to provide a new one: pacta sunt servanda and bona fides to one's own consent. Under the new law of nations, ratification by oath was just another form of expressing the consent which bound a ruler to a treaty. Gradually, it was superseded and then totally replaced as the main constitutive element of the treaty by the exchange of signed and sealed documents. Between the 15th and 20th centuries, the mechanisms used to safeguard the peace evolved. Until the end of the 17th century, most peace treaties expressly stipulated that a violation of the treaty by a subject would not lead to a breach of the peace, but that the perpetrator would be punished and restitution would be done.48 Peace treaties of the 16th and 17th centuries often provided for the appointment of special commissioners or arbitrators to resolve conflicts about the interpretation and execution of the treaty, as well as work out some outstanding issues.49 Before the Reformation, ecclesiastical jurisdiction and sanctions had been the strongest and most general mechanism to enforce the peace upon the treaty parties. The use of hostages was fairly uncommon and it was mainly used to guarantee the execution of particular clauses in peace treaties, such as the surrender of territories, towns, or fortresses or money payments. Sometimes, princes pledged all their goods to the treaty, thus giving the treaty partner a claim to lawfully seize these goods in case of a breach of treaty and the resulting new war. By the mid-17th century, these practices had largely fallen into disuse. Between the mid-17th and the mid-18th centuries, treaty partners frequently made use of guarantors. A guarantee implied that a power would enforce the treaty upon the treaty partners, if necessary through the use of force. A distinction can be made between guarantees from treaty partners and guarantees from third (p. 84) powers. The first form only makes sense for multilateral peace treaties, which were very uncommon until the mid-18th century. The main exceptions are—seemingly—the two Peace Treaties of Westphalia (24 October 1648)—that of Münster between the empire and France, and of Osnabrück between the empire and Sweden—to which not only the emperor and the king of France, respectively the queen of Sweden, but also a great number of imperial Estates acceded.50 More frequent were guarantees by third powers. Some of the peace treaties coming out of the great peace conferences from the late 17th and 18th centuries invited the powers which had acted as mediators to become guarantors.51 Guarantees in peace treaties fell into disuse during the second half of the 18th century. Special treaties of guarantee whereby powers promised their support for the upholding of certain rights became more common over the 19th century. That century also saw the emergence of new enforcement means for peace treaties, which would survive into the 20th century. These were mostly of a military nature such as the (temporary) occupation of part of the territory or the imposition of military restrictions.52

5.  Perpetual and General Peace

5.1.  Perpetual Peace

Most peace treaties from the 16th to the early 19th century expressly stated that peace would be perpetual. This was not the—seemingly stubborn and naïve—expression of a legal commitment never to resort to war again, but held more specific implications under the law of nations. Already the medieval civilians had acknowledged that if a new war broke out between treaty partners for a new cause, other than the one underlying the previous war which had been settled in the peace treaty, this did not constitute a breach of the treaty.53 From this, one can deduce e contrario that a peace treaty exhausted the right of the former belligerents to resort to armed force over the disputes settled in the peace treaty. But it would take Samuel Pufendorf (1632–94),54 (p. 85) Wolff, and Vattel to state it so straightforwardly.55 The perpetual character of a peace distinguished it from a truce. A truce could, as much as a peace treaty, put an end to all measures that had been taken at the inception of the war, and thus for all practical purposes suspend the state of war and restore the state of peace, but parties had the right to resort to war for the same issues once the truce had lapsed.

5.2.  General Peace

Before the Peace of Aachen (1748), peace treaties were almost always bilateral.56 This was as true for peace treaties made at general, multilateral peace conferences. The Peace Treaties of Münster and Osnabrück (24 October 1648) were not truly exceptions to the rule. Their multilateral character was consequential to their hybrid nature: they were at once international peace pacts between the empire and France or Sweden respectively as well as internal peace compacts between the emperor and the Estates of the Holy Roman Empire. As international peace compacts, they were not different from regular, bilateral peace treaties, both in form as in substance. Their much-acclaimed contribution to the development of the law of nations and the constitution of Europe stems from the fact that their hybrid nature caused constitutional settlements which pertained to the Empire to seep into international treaties and thus find their way into the law of nations.57

Some peace treaties of the early-modern age, particularly those coming out of multilateral peace conferences, were expressly said to inaugurate a ‘universal’ peace, under which term Christian Europe was meant.58 These claims to universality seem to be corroborated by the custom to ‘include’ numerous third powers into the treaties. But one should be careful not to overstate the implications of these inclusions. Inclusion clauses were very common in peace treaties between the 15th and 18th centuries and were certainly not limited to so-called universal peace treaties or peace treaties from multilateral conferences. With these clauses, treaty partners associated their allies and auxiliaries to the peace treaty. In some of the important peace treaties, almost all important powers were included. An in-depth study of diplomatic practice would have to show what the exact legal implications of inclusion were, but it is clear that it did not amount to full accession. The main effect of (p. 86) inclusion was that it committed the treaty partner not to enact retribution against the allies of its former enemy. In the 17th and 18th centuries, inclusion had most relevance in relation to auxiliary powers. Inclusion protected States which had supported a certain side in the war—with money or troops—without being openly at war. Inclusion did not make the whole treaty applicable to the included power nor granted it the same rights and imposed the same obligations—which would be impractical without particular negotiations—but extended the general clause of peace and amity to the included power. Inclusion did not suffice to restore peace between powers that were actually at war with one another. For this, a separate peace treaty or full accession to a peace treaty was necessary.59 Some peace treaties of the 17th and 18th centuries referred back to older peace treaties. This has been indicated in modern scholarship as proof for their constitutional role in the European States system. Until the end of the 17th century, references to previous peace treaties as ‘base and foundation’ of a new treaty were restricted to the Holy Roman Empire. The first treaties to be mentioned thus way were the Westphalian Treaties.60 This was in fact a consequence of these Treaties having been declared imperial law.61 However, the practice took hold in international relations and became general in the 18th century. The Peace Treaty of Paris of 10 February 1763 named the Treaties of Westphalia, Nijmegen, Ryswick, Utrecht, Baden (1714), Vienna (1738), Aachen (1748), as well as the Triple and Quadruple Alliances (1717/18), and some particular treaties between Great Britain and Spain and Portugal and Spain as ‘base and foundation’.62 These treaties can indeed be considered ‘constitutional’ to the order of Europe to the extent that they settled major dynastic and territorial disputes and reflected some of the leading principles of European order. But, formally speaking, they were just regular treaties without any superior authority. In fact, in most cases, it was expressly stated that these treaties were renewed and were to be held applicable as if they were inserted ‘word for word’ in the new treaty, at least inasmuch as it did not derogate from it.63 These older treaties were not paramount law in relation to the new treaty, as any special position they had derived from the new treaty.

The notion of ‘universal peace’ was relevant in yet another way. The preambles of peace treaties often indicate which ulterior purposes the treaty partners had in making peace. From the vast majority of peace treaties from the 15th to the 20th centuries, it appears that the powers of Europe considered a general peace within Christianity (p. 87) (15th–18th centuries) or Europe (17th–20th centuries) the ultimate purpose of their endeavours and their common responsibility. To this, the particular, generally bilateral peace treaty was said to contribute, and treaty parties implicitly explained their willingness to grant concessions in these terms. The goal of general peace was associated with other goals or principles which evolved over time. In the 15th and early 16th centuries, it was linked to the need for unity of the Christian world in the face of the Turkish threat. In the late 17th and 18th centuries, mention was made of the ‘tranquility and security of Europe’. This referred to the need to uphold the dynastic and territorial status quo as laid down in great peace compacts. Although express references to the balance of power were rare, it was considered a necessary precondition for the tranquility and security of Europe.64 During the 18th and 19th centuries, it became accepted that the great powers held a particular responsibility, and therefore special rights, to uphold the peace and security of Europe. The Triple and Quadruple Alliances of 1717–18 and some treaties of guarantee of the 18th century offer early expressions thereof. In the 19th century, the great powers assumed their role through the Congress of Europe, whereby regular multilateral conferences were convened to decide about major issues of peace and security and wherein the great power took a dominant role. This ‘great power principle’ was later institutionalized in the Council of the League of Nations (1919) and the Security Council of the United Nations Organisation (1945).65

6.  Just and Formal War, Just and Formal Peace

Under a consequential application of the just war doctrine, a just war needed to end in a just peace. Wolff and Vattel spelled out the multiple, far-reaching consequences thereof. First, it meant that the unjust belligerent lost his claim to the object over which the war was fought. Second, he was liable for all the damages and costs suffered by the just belligerent because of the war. Under the just war doctrine, the (p. 88) unjust belligerent could not benefit from the full protection of the ius in bello; all hostile actions by the unjust belligerent were unjust actions for which he was liable. Third, the just belligerent was also liable for his unjust wartime actions—that is, actions that went against the laws of war.66 But Wolff and Vattel found this totally impractical as in most cases it was impossible to discern who held just cause, and it could not be expected that sovereigns would subject themselves to the judgment of their peers. As most writers had done since Grotius, Wolff and Vattel banished the justice of war into the sphere of natural law, which was only enforceable in conscience. The externally enforceable law of nations only dealt with the question of the legality of the war. The peace that answered to such a formal or legal war would not have to deal with the question of justice but would be a compromise reached through negotiation and sanctioned by the consent of the parties. By applying the distinction between natural and positive law to just and legal war, Grotius—who built on the ideas of the Spanish neo-scholastics—and his successors gave both medieval traditions of the ius ad bellum, the canonical theologian tradition of just war and the civilian tradition of legal war, a place in early-modern doctrine. But more to the point, this duality reflected the duplicity of reality. On the one hand, the doctrine of just war still held sway among the sovereign princes of early-modern Europe, as they continued to justify their wars in terms of the justice of their cause. Declarations and manifestos of war as well as alliance treaties clearly drew on the traditions of just war. Some hostile measures against the enemy, such as the seizure of private property, were at least implicitly justified by the acclaimed justice of the war. But on the other hand, during war, belligerents applied the laws of war to all belligerents without any discrimination for the justice or injustice of their respective positions. Neither did claims to the justice of the war play any role in the making of peace, at least not among European sovereigns.67 In other words, the sovereign powers of Europe went to just war, fought a formal war, and made a formal peace. Some examples of peace treaties which can be considered ‘just’ can be quoted from antiquity and the Middle Ages. Generally but not exclusively, such peace treaties were only made after a clear victory or in the context of a hierarchical relation.68 Typically, such treaties contained an express judgment on the justice of the war and attributed the responsibility for the war to one of the belligerents. The concessions the ‘unjust’ side had to make came as a result of the injustice of his cause or actions during the war. Compensations for the mere act of having fought an unjust war and/or for the damages and costs of the war were often imposed, mostly in the form of a tribute. In some cases, restrictions on the military capacity of the unjust belligerent were provided, in order to prevent him from resorting to war again. None of the peace treaties between European sovereigns of the 16th to early 20th centuries was of that type. In (p. 89) not a single peace treaty was judgment rendered on the justice of the war, nor did a single treaty contain an attribution of guilt to one of the belligerents. In the preambles to peace treaties, the signatories most often limited themselves to deploring the war and the hardship it had brought in the most general terms. This was different for part of the peace treaties made between European and non-European rulers. Particularly in the Americas, the European powers styled peace treaties as unilateral grants of peace. The treaties laid the blame for the war, which was often labelled a rebellion, at the doorstep of the indigenous peoples. Amnesty was a unilateral act of mercy, which had to be paid for through cessions and tributes.69 The absence of any judgment on the justice of war meant that concessions could not be explained in terms of the injustice of a belligerent's cause for war or the underlying claims about conceded rights and territories. Neither were express references made to a right of conquest—although this was often implied and the right of conquest was a contrario upheld in some peace treaties.70 Hardly the only justifications which were ever offered, and very rarely so, were general references to the interest of a stable and enduring peace and friendship.71 The basis for treaty concessions was ultimately nothing but the consent of the parties. The refusal to judge was not restricted to the level of the ius ad bellum, but extended to the ius in bello. From the late 15th century onwards, it became customary for the signatories to include a clause of amnesty and oblivion in the treaty. This implied that the signatories waived all claims for damages and costs because of the war, for themselves as well as for their subjects.72 By the beginning of the 19th century, these clauses disappeared, but by then it had become accepted that they were automatically implied.73 The amnesty clause was tied in with another common stipulation, relating to the restitution of private property. During the early-modern age, it was customary for the belligerents to seize the property of enemy subjects found on their territory. Under the just war doctrine, this was done to safeguard the future payment of the damages and the costs of war caused by the unjust belligerent. As peace treaties did not render judgment on the justice of war, the legal basis for their seizure collapsed. Therefore, most peace treaties included a general clause of automatic restitution. To this standard provision, treaties also made a standard exception for movables.74

(p. 90) 7.  The Expansion of European Peace Treaty Practice

Until the 19th century, the European law of nations with its practices and laws of peacemaking was but one of several regional systems. Other civilizations developed their own regional systems of peacemaking and peace treaties.

Since the 8th century, the Latin West and the Islamic world had been in constant contact. The discoveries and the early empire-building by Europeans from the late 15th century onwards expanded the scope of Europe's international relation to America, sub-Saharan Africa and Asia. But for a long time, this did not lead to the expansion of the European legal order to other parts of the world. Instead, we can discern two different patterns of behaviour. First, in some cases, contacts and wars between Europeans and non-Europeans led to the articulation of a peace treaty practice which built on the practices and laws of the two civilizations involved, forming a kind of supra-regional system particular to their mutual relations. This was the outcome when Europeans had to deal with powerful contenders, such as the Arab rulers in the Middle Ages, the Ottoman Empire, or the princes and empires of India and East and South-East Asia. Second, when European powers were in a position to impose their will, as was often the case in the Americas or Africa, they imposed a particular design of treaties which was different from that used among European sovereigns. These often included attributions of guilt for the war as well as total subjection or the imposition of harsh conditions on the basis of the indigenous people's one-sided responsibility for the conflict.75

The achievement of independence by the white settler colonies of America around 1800 expanded the European law of nations and its system of peacemaking over the Atlantic. The Peace of Paris (1856)76 expressly stipulated that the Ottoman Empire would enjoy the advantages of the public law and the Concert of Europe. In the middle of the 19th century, the European power and the United States forced China and Japan into their systems of international law and forced Western peace treaty practices upon them. The decolonization of the 20th century made Western international law and its peace treaty practices truly global.

(p. 91) 8.  The Transformation of PeaceTreaty Practice and Law after theFirst World War

Versailles and the other Parisian peace treaties at the end of the First World War (1919–20) mark a sudden break in European peace treaty practice. To some extent, they constitute a return to a concept of just peace. Article 231 of the Versailles Treaty put the blame for the war on Germany because of its acts of aggression. Article 232 imposed upon Germany the obligation to pay compensation for all damage done to civilians and their property, as well as compensate for the debts of Belgium to its allies for its war costs. In itself, the imposition of compensation for the costs and damages of war by the victor upon a defeated power were not new. They had been introduced during the Napoleonic Wars and had been provided for in important peace treaties such as those of Paris (1814–15) and Frankfurt (1871).77 These compensations had in no way been related to an attribution of guilt for the war but were merely consequential to the defeat. The return to a concept of ‘just peace’ went even further in the Versailles Peace Treaty. In the Treaty, the German Emperor was made liable to criminal prosecution for his ‘supreme offence against international morality and the sanctity of treaties’ through his aggression (article 227). The Treaty also provided for the criminal prosecution by the Allied and Associated Powers of Germans for violations against the laws and customs of war (article 228). Furthermore, it imposed severe military restrictions on Germany.78

The return to just peace was not followed through after Versailles. Throughout the 20th century, most interstate peace treaties were still formal peace treaties without attributions of guilt. But the peace treaties with the European allies of Germany (Paris 1947) after the Second World War applied a sort of concept of just peace. The same goes for the conditions for ending the hostilities imposed upon Iraq by the United Nations Security Council (Resolution 687)79 at the end of the First Gulf War (1991).80

Twentieth-century peace practice saw more fundamental changes than this partial revival of just peace. First, the relative number of interstate armed conflicts ended by peace treaties seriously declined after 1945. In some cases, as that of Germany after the Second World War, this was due to political circumstances. But more generally, this decline was consequential to a change in the concept of war. The outlawing of war—in the Kellogg–Briand Pact (1928)81 and the UN Charter—has caused a sharp decline in (p. 92) the number of formally declared ‘legal wars’. Under the post-Charter ius ad bellum, the distinction between the state of war and a state of peace has become more relative and ‘wars’ are again perceived in terms of separate acts of war or hostility rather than as an all-encompassing legal state. For this reason, the traditional peace treaty has fallen into relative disuse. But whereas this is often seen as the demise of peace treaty practice, it can as readily be considered part of a process of its transformation. Formal peace treaties marking the transit from state of war to state of peace may have become relatively rare but have not disappeared altogether.82 As legal forms and concepts of interstate armed conflict became more varied, legal forms and contents of agreements to end them likewise became more varied. Some conflicts ended with an armistice and/or a preliminary agreement whereby relations quickly or gradually regained a level of normalcy. In other cases, treaties of friendship organizing aspects of the relations between belligerents were used without a formal end to the war being expressly declared.83

Second, the years since 1945 have been marked by a proliferation of intra-state armed conflicts, in which third powers were often involved. In this context, hundreds of peace agreements were made. These agreements often take the form of international treaties but are mostly hybrid in nature, because they span inter- and intra-state affairs. More than being instruments of conflict resolution, current peace agreements are as much instruments of constitutional formation that break through the confines of domestic and international order. They include detailed regulations of constitutional (re-)formation.84

Third, next to State building, another important issue has come to expand the concern of peacemaking—or peace building as it is now called—and widened the domain of the ius post bellum: the protection of human rights. This has started with the inclusion of stipulations on minority rights in the late 19th century.85 By the late 20th century, this has come to include stipulations on general human rights, including political and economic rights as well as on the prosecution of violations against international humanitarian law.86

Fourth, peacemaking turned into a drawn-out process of peace building, implying a series of agreements and documents. This is not completely new as also in the early-modern age use was made of armistices and preliminary peace treaties in preparation (p. 93) of the peace treaty as well as particular treaties following up on different aspects of peacemaking. But then, there had always been a formal peace treaty at the centre which marked the momentary transition from war to peace. As war and peace have become relative concepts, so the notion of a sudden transition has made place for that of a transition process.

9.  Conclusion

Early-modern Europe developed a particular kind of peace treaty practice and law which was premised on the sovereign State in three ways. First, the sovereign State monopolized the right to make peace treaties. Second, a formal concept of war was introduced which excluded all notions of justice and discrimination on the basis of justice in the waging of war (ius in bello) and the making of peace (ius post bellum). Third, the collapse of supra-state authorities gave consent through treaty a central role in the articulation of general as well as particular law of nations. Peace treaties naturally were most relevant to the development of the ius post bellum. The 20th century saw the relative demise of the sovereign state in international law, and changed the law and practice of peacemaking. The traditional formal interstate peace treaty lost its quasi-monopoly as legal instrument of peacemaking. Instead a variety of peace agreements emerged. Moreover, the boundaries between inter- and intra-state peacemaking became transparent again and the ius post bellum expanded into a ius post bellum encompassing the protection of human rights and state building.

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1  Q Wright A Study of War (5 vols Chicago University Press Chicago 1942); Q Wright ‘How Hostilities Have Ended: Peace Treaties and Alternatives’ (1970) 392 Annals of the American Academy of Political and Social Science 51–61.

2  A Osiander The States System of Europe, 1640–1990: Peacemaking and the Conditions of International Stability (OUP Oxford 1994).

3  Cicero (106–43 BC) Pro Balbo 6.15.

4  C Baldus ‘Vestigia pacis. The Roman Peace Treaty: Structure or Event?’ in R Lesaffer (ed) Peace Treaties and International Law in European History: From the Late Middle Ages to World War One (CUP Cambridge 2004) 103–46; DJ Bederman International Law in Antiquity (CUP Cambridge 2001) 137–206; H Bengtson Die Staatsverträge des griechisch-römischen Welt von 700 bis 338 v. Chr (Die Staatsverträge des Altertums) (CH Beck Munich 1962) vol 2; HH Schmitt Die Verträge der griechisch-römischen Welt von 338 bis 200 v. Chr (Die Staatsverträge des Altertums) (CH Beck Munich 1969) vol 3; KH Ziegler ‘Conclusion and Publication of International Treaties in Antiquity’ (1995) 29 Israel Law Review 233–49; KH Ziegler ‘Friedensverträge im römischen Altertum’ (1989) 27 Archiv des Völkerrechts 45–62.

5  Isidorus of Seville (c 560–636) Etymologiae 5.6.

6  See Aulus Gellius (2nd century BC) Noctes Atticae 1.25.4: ‘neque pax est indutiae—bellum enim manet, pugna cessat’ (‘and an armistice is neither peace—for the state of war endures; fighting stops’) (trans by the author); KH Ziegler ‘Kriegsverträge im antiken römischen Recht’ (1985) 100 Savigny Zeitschrift für Rechtsgeschichte Romanistische Abteilung 40–90.

7  Glossa Paciscuntur ad D. 2.14.5: ‘ut treugas, quae sunt in longum tempus. Item inducias, quae sunt in breve’ (‘such as truces, which are made for a long time. Further armistices, which are made for a short time’) and Glossa Lacessant ad ‘ … Sed treugae in longum, et dicuntur foedera, (‘But truces are for a long time, and they are called treaties’). See also Glossa Foederati ad D. 49.15.7.

8  B Paradisi ‘L’organisation de la paix au IVe et Ve siècles’ in B Paradisi Civitas maxima. Studi di storia del diritto internazionale (Olschki Florence 1974) vol 1, 236–95.

9  Decretal Novit Ille by Innocent III (1198–1216) in Liber Extra (1234) X. 2.1.13.

10  Eg Traité de Paix entre Charles VIII, Roi de France et Henri VII, Roi d’Angleterre, fait à Etaples (3 November 1492) in J Dumont Corps universel diplomatique du droit des gens (Brunel Amsterdam 1726) (hereinafter CUD) vol 3:2, 291–7, art 28.

11  Eg Traité, ou Trêves Marchandes faites pour neuf ans entre Louis XI, Roi de France et Charles, dernier Duc Bourgogne, fait à Soleuvre (13 September 1475) in CUD (n 10) vol 3:2, 508, in fine.

12  Most significant is MG Laudensis ‘De confoederatione, pace et conventionibus principum’ (15th century) (A Wijffels ed) in Peace Treaties and International Law (n 4) 412–47.

13  Baldus de Ubaldis (1327–1400), see B de Ubaldis Super usibus feudorum et commentum super pace Constantiae (F Patavinus ed) (in domo Antonii et Raphaelis de Vulterris Rome 1474); G Dolezalek ‘I commentari di Odofredo e Baldo alla pace di Constanza’ in La pace di Costanza 1183 (Cappelli Bologna 1984) 59–75.

14  KH Ziegler ‘The Influence of Medieval Roman Law on Peace Treaties’ in Peace Treaties and International Law (n 4) 147–61.

15  Liber Extra (n 9) X. 1.34.

16  See Tractatus universi juris (F Ziletti Venice 1583–86) vol 11.

17  Liber Extra (n 9) X. 1.35.1; R Lesaffer ‘The Medieval Canon Law of Contract and Early Modern Treaty Law’ (2000) 2 Journal of the History of International Law 178–98; KH Ziegler ‘Biblische Grundlagen des europäischen Völkerrechts’ (2000) Savigny Zeitschrift für Rechtsgeschichte Kanonistische Abteilung 1–32.

18  L Bittner Die Lehre von den völkerrechtlichen Vertragsurkunden (Deutsche Verlags-Anstalt Stuttgart 1924); A Hertz ‘Medieval Treaty Obligation’ (1991) 6 Connecticut Journal of International Law 425–43; A Nussbaum ‘Forms and Observance of Treaties in the Middle Ages and the Early Sixteenth Century’ in GA Lipsky (ed) Law and Politics in the World Community: Essays on Hans Kelsen's Pure Theory and Related Issues in International Law (University of California Press Berkeley 1953) 191–6;, ‘Influence of Medieval Roman Law’ (n 14) at 152–4. On signed and sealed documents, see R Lesaffer ‘Peace Treaties from Lodi to Westphalia’ in Peace Treaties and International Law (n 4) 9–44 at 25–7; H Steiger ‘Bemerkungen zum Friedensvertrag von Crépy en Laonnais vom 18. September 1544 zwischen Karl V. und Franz I.’ in U Beyerlin et al (eds) Recht zwischen Umbruch und Bewahrhung: Völkerrecht—Europarecht—Staatsrecht. Festschrift für Rudolf Bernhardt (Springer Berlin 1995) vol 2, 249–65 at 256–60.

19  J Barnes ‘The Just War’ in N Kretzman et al (eds) The Cambridge History of Later Medieval Philosophy (CUP Cambridge 1982) 750–84; P Haggenmacher Grotius et la doctrine de la guerre juste (Presses Universitaires de France Paris 1983); FH Russell The Just War in the Middle Ages (CUP Cambridge 1975).

20  See the contributions by M Scattola ‘Alberico Gentili (1552–1608)’ and by P Haggenmacher ‘Hugo Grotius (1583–1645)’ in this volume.

21  Eg H Grotius De jure belli ac pacis libri tres (1625) at ‘But Custom had so prevailed, that not the Act of Hostility, but the State and Situation of the Contending Parties, now goes by the Name; so that War is the State or Situation of those (considered in that Respect) who dispute by Force of Arms.’ H Grotius The Rights of War and Peace (R Tuck ed, J Morrice trans) (3 vols Natural Law and Enlightenment Classics Liberty Fund Indianapolis 2005).

22  S Whatley (ed) A General Collection of Treatys, Declarations of War, Manifestos, and other Publick Papers, Relating to Peace and War, Among the Potentates of Europe, from 1648 to the Present Time (4 vols Knapton etc London 1710–32); R Lesaffer ‘Defensive Warfare, Prevention and Hegemony. The Justifications for the Franco-Spanish War of 1635’ (2006) 8 Journal of the History of International Law 91–123 and 141–79 at 111–23; SC Neff War and the Law of Nations: A Historical Survey (CUP Cambridge 2005) at 54–68 and 96–119.

23  SC Neff ‘Peace and Prosperity: Commercial Aspects of Peacemaking’ in Peace Treaties and International Law (n 4) 365–81; H Steiger ‘Peace Treaties from Paris to Versailles’ in Peace Treaties and International Law (n 4) 59–99 at 94–6.

24  Treaty of Peace between the Allied and Associated Powers and Germany (signed 28 June 1919) (1919) 225 CTS 188 (‘Treaty of Versailles’).

25  KH Ziegler ‘Römische Grundlagen des europäischen Völkerrechts’ (1971) 4 Ius commune 1–27 at 16–27.

26  Exceptions include P Gudelinus De jure pacis commentarius (Dormalius Leuven 1620); see R Lesaffer ‘An Early Treatise on Peace Treaties: Petrus Gudelinus between Roman Law and Modern Practice’ (2002) 23 Journal of Legal History 223–52.

27  See the contributions by K Haakonssen ‘Christian Wolff (1679–1754)’ and by E Jouannet ‘Emer de Vattel (1714–1767)’ in this volume.

28  A Gentili De jure belli libri tres in JB Scott (ed) Classics of International Law (2 vols OUP Oxford 1933) book 3, ch 1; C Wolff Jus gentium methodo scientifica pertractatum in JB Scott (ed) Classics of International Law (2 vols Clarendon Oxford 1934);E de Vattel Le droit des gens ou principes de la loi naturelle in JB Scott (ed) Classics of International Law (3 vols Carnegie Washington 1916); R Phillimore Commentaries upon International Law (3rd edn Buttersworths London 1879–89) vol 3, at 770–811; P Fauchille Traité de droit international public (Rousseau Paris 1921–23) vol 2, at 1030–59; see R Lesaffer ‘Alberico Gentili's ius post bellum and Early Modern Peace Treaties’ in B Kingsbury and B Straumann (eds) The Roman Foundations of the Law of Nations: Alberico Gentili and the Justice of Empire (OUP Oxford 2010) 210–40; R Lesaffer ‘A Schoolmaster Abolishing Homework? Vattel on peacemaking and peace treaties’ in V Chetail and P Haggenmacher (eds) Vattel's International Law in XXIst Century Perspective/Le droit international de Vattel vu du XXIe siècle (Brill Leyden 2011) 353–84.

29  Treaty of Peace between Spain and the Netherlands (signed 30 January 1648) (1648) 1 CTS 1, art 21.

30  The Peace of Münster: Treaty of Peace between Spain and the Netherlands (n 29). The Treaties of Münster: Treaty of Peace between the Holy Roman Empire and France (signed 24 October 1648) (1648) 1 CTS 271; and Osnabrück: Treaty of Peace between the Holy Roman Empire and Sweden (signed 24 October 1648) (1648) 1 CTS 198. Together these treaties form the Peace of Westphalia.

31  H Bots (ed) The Peace of Nijmegen 1676–1678/79/La paix de Nimègue 1676–1678/79 (Holland Universiteits Pers Amsterdam 1980) (proceedings of the conference marking the tricentennial anniversary of the Treaties of Nijmegen, Nijmegen, 14–16 September 1978).

32  Treaty of Peace Between France and The Netherlands (signed 20 September 1697) (1697) 21 CTS 347.

33  Treaty of Peace and Friendship Between France and Great Britain (signed 11 April 1713) (1713) 27 CTS 477 (‘Treaty of Utrecht’); Treaty of Peace Between the Emperor and Spain, and France (signed 7 March 1714) (1714) 29 CTS 1 (‘Treaty of Rastatt’).

34  Treaty of Aix-la-Chapelle (signed 18 October 1748) (1748) 38 CTS 297.

35  Definitive Treaty of Peace and Friendship between France, Great Britain and Spain (signed 10 February 1763) (1763) 42 CTS 279; Treaty of Peace between Austria and Prussia (signed 15 February 1765) 42 CTS 347.

36  J Fisch Krieg und Frieden im Friedensvertrag: Eine universalgeschichtliche Studie über die Grundlagen und Formelemente des Friedensschlusses (Klett-Cotta Stuttgart 1979) at 536–7; R Lesaffer ‘Charles V, monarchia universalis and the Law of Nations (1515–30)’ (2003) 71 Legal History Review 79–123; ‘Gentili's ius post bellum’ (n 28) 212–13; R Lesaffer and EJ Broers ‘Private Property in the Dutch-Spanish Peace Treaty of Münster (30 January 1648)’ in M Jucker et al (eds) Rechtsformen Internationaler Politik: Theorie, Norm und Praxis vom 12. bis 18. Jahrhundert (Zeitschrift für Historische Forschung Beihefte Duncker & Humblot Berlin 2011); ‘Friedensvertrag von Crépy’ (n 18).

37  Traité de Paix entre Louis XI, Roi de France d’une part, Charles Comte de Charlois et les Princes Liguez, sous le nom du Bien d’autre part, fait à Conflans (5 October 1465) in CUD (n 10) vol 3:1, 335–7.

38  Edit de Henri IV, Roi de France par la Pacification des Troubles de son Royaume, fait à Nantes (April 1598) in CUD (n 10) vol 5–1, 545–58, Preamble.

39  Still in Treaty of Peace between Bulgaria, Greece, Montenegro, Serbia and Turkey (signed 30 May 1913) (1913) 218 CTS 159 and Treaty of Peace between Bulgaria, Greece, Montenegro, Romania and Serbia (signed 19 August 1913) (1913) 218 CTS 322. The first peace treaty mentioning States is the Treaty of Peace between France and Germany (signed 10 May 1871) (1871) 143 CTS 163.

40  J Ray ‘La communauté internationale d’après les traités du XVIe siècle à nos jours’ (1938) 3 Annales Sociologiques, series C, 14–49 at 19.

41  Treaty of Peace between Spain and the Netherlands (n 29) Preamble.

42  Treaty of Campo Formio (signed 17 October 1797) (1797) 54 CTS 157 at 158, Preamble.

43  Appunctuamenta amicitiae perpetuae inter Carolum Audacem, Ducem Burgundiae et Eduardem IV, Regem Anglicae (25 July 1474) in CUD (n 10) vol 3:1, 485–6, Preamble.

44  Etaples (n 10) art 1.

45  Traité de Paix entre Henri II, Roi de France et Filippe II, Roi d’Espagne, fait à Câteau-Cambrésis (3 April 1559) CUD (n 10) vol 5:1, 34–44 at 41, art 47.

46  Traité de Paix entre Louis XI, Roi de France, le Dauphin et le Royaume d’une part et Maximilien, Duc d’Autriche, Mr le Duc Philippe et Mademoiselle Marguerite d’Autriche d’autre part: Contenant entr’autres, un Accord de Mariage entre ledit Prince Dauphin et ladite Princesse Marguerite (23 December 1482) CUD (n 10) vol 3:2, 100–10 at 107, art 88. Divergent view, K Neitmann Die Staatsverträge des deutschen Ordens in Preussen 1230–1449: Studien zur Diplomatie eines spätmittelalterlichen deutschen Territorialstaates (Neue Forschungen zur brandenburg-preussischen Geschichte 6) (Böhlau Cologne 1986) at 276–81.

47  Traité de Paix entre Henri IV, Roi de France, Philippe II, Roi d’Espagne et Charles-Emanuel, Duc de Savoie, fait à Vervin (2 May 1598) in CUD (n 10) vol 5:1, 561–9 at 564, in fine.

48  Treaty of Peace between England and the Netherlands (5 April 1654) (1654) 3 CTS 225 at 234–5, art 24.

49  Treaty of Peace between Spain and the Netherlands (n 29) art 21.

50  Treaty of Peace between France and the Empire (signed 24 October 1648) (1648) 1 CTS 271 at 354, para 124 and Treaty of Peace between Sweden and the Empire (signed 24 October 1648) (1648) 1 CTS 198, art 17(4).

51  Treaty of Peace of Nijmegen (signed 10 August 1678) (1678) 14 CTS 365 at 374, art 20. H Duchhardt ‘Peace Treaties from Westphalia to the Revolutionary Era’ in Peace Treaties and International Law (n 4) 45–58 at 55.

52  ‘Peace Treaties from Paris to Versailles’ (n 23) 91–2.

53  Baldus de Ubaldis Consilium 2.195. See ‘Gentili's ius post bellum’ (n 28) 227.

54  See the contribution by K Haakonssen ‘Samuel Pufendorf (1632–1694)’ in this volume.

55  S Pufendorf De jure naturae et gentium libri octo (CH and WA Oldfather trans) (2 vols Classics of International Law Clarendon Oxford 1934) 8.7.4; Jus gentium (n 28) 8.987; Droit des gens (n 28) 4.2.19.

56  K Marek ‘Contribution à l’étude de l’histoire du traité multilatéral’ in E Diez et al (eds) Festschrift für Rudolf Bindschedler (Stämpfli Bern 1980) 17–39.

57  R Lesaffer ‘The Westphalia Peace Treaties and the Development of the Tradition of Great European Peace Settlements prior to 1648’ (1997) 18 Grotiana NS 71–95; H Steiger ‘Der westfälische Frieden—Grundgesetz für Europa?’ in H Duchhardt (ed) Der westfälische Friede: Diplomatie, politische Zäsur, kulturelles Umfeld, Rezeptionsgeschichte (Oldenbourg Munich 1998) 33–80.

58  Treaty of Peace between France and the Empire (n 50) 321–2, para 1.

59  Jus gentium (n 26) 8.1009; Droit des gens (n 28) 4.2.15; R Lesaffer ‘Amicitia in Renaissance Peace and Alliance Treaties’ (2002) Journal of the History of International Law 4 77–99; ‘Westfälischer Frieden’ (n 57) at 45–8.

60  Of the Peace Treaties made at Ryswick the one between the Empire and France was the only one to mention Westphalia and Nijmegen (30 October 1697) (1697) 22 CTS 5, art 3.

61  Treaty of Peace between France and the Empire (n 50) 353, para 120 and Treaty of Peace between Sweden and the Empire (n 50) art 17(2).

62  Definitive Treaty of Peace between France, Great Britain and Spain (n 35) art 2.

63  Treaty of Aix-la-Chapelle (n 34) art 3.

64  H Duchhardt ‘The Missing Balance’ (2000) 2 Journal of the History of International Law 67–72; R Lesaffer ‘Paix et guerre dans les grands traités du XVIIIe siècle’ (2005) Journal of the History of International Law 7 25–41 at 37–40.

65  R Lesaffer ‘The Grotian Tradition Revisited: Change and Continuity in the History of International Law’ (2002) 73 British Yearbook of International Law 103–39 at 133–5; States System of Europe (n 2) 321–30; G Simpson Great Powers and Outlaw States: Unequal Sovereigns in the International Legal Order (CUP Cambridge 2004) at 91–131.

66  Jus gentium (n 28) 8.986; Droit des gens (n 28) 4.2.18.

67  ‘Gentili's ius post bellum’ (n 28) 237–40; ‘A Schoolmaster Abolishing Homework’ (n 28).

68  Krieg und Frieden (n 36) 69–70 and 81–8.

69  Krieg und Frieden (n 36) 139–204.

70  Treaty of Berlin between Hungary and Prussia (signed 28 July 1742) (1742) 36 CTS 409 at 414–16, art 5; Definitive Treaty of Peace between France, Great Britain and Spain (n 62) art 23. S Korman The Right of Conquest: The Acquisition of Territory by Force in International Law and Practice (OUP Oxford 1996) at 67–73.

71  Definitive Treaty of Peace between France, Great Britain and Spain (n 35) art 7.

72  Krieg und Frieden (n 36) 92–123.

73  De jure belli ac pacis (n 21) 3.20.15; Jus gentium (n 28) 8.990; Droit des gens (n 28) 4.2.20.

74  H Neufeld The International Protection of Private Creditors from the Treaties of Westphalia to the Congress of Vienna: A contribution to the history of the law of nations (Sijthoff Leyden 1971).

75  CH Alexandrowicz ‘Treaty and Diplomatic Relations Between European and South Asian Powers in the Seventeenth and Eighteenth Centuries’ (1960) 100 Recueil des Cours de l’Académie de Droit International 207–320; CH Alexandrowicz An Introduction to the Law of Nations in the East Indies 16th, 17th and 18th Centuries (Clarendon Oxford 1967); CH Alexandrowicz The European–Africa Confrontation: A Study in Treaty Making (Sijthoff Leyden 1973); J Fisch Die europäische Expansion und das Völkerrecht. Die Auseinandersetzungen um den Status der überseeischen Gebiete vom 15. Jahrhundert bis zur Gegenwart (Steiner Stuttgart 1984); FP Prucha American Indian Treaties: The History of a Political Anomaly (University of California Press Berkeley 1994); KH Ziegler ‘The Peace Treaties of the Ottoman Empire with European Christian Powers’ in Peace Treaties and International Law (n 4) 338–64.

76  General Treaty for the Re-Establishment of Peace between Austria, France, Great Britain, Prussia, Sardinia, Turkey and Russia (signed 30 March 1856) (1856) 114 CTS 409, art 7.

77  Treaty of Frankfurt between France and Prussia (signed 10 May 1871) (1871) 143 CTS 166, art 7.

78  Treaty of Versailles (n 24).

79  UNSC Res 687 (3 April 1991) UN Doc S/Res/687.

80  G Fitzmaurice ‘The Juridical Clauses of the Peace Treaties’ (1948) 73 Recueil des cours 259–367 at 262–8; R Lesaffer Europa: een zoektocht naar vrede? (1453–1763 en 1945–99) (Europe: A Quest for Peace? (1453–1763 and 1945–99)) (Universitaire Pers Leuven Leuven 1999) at 562–7; M Weller Iraq and the Use of Force in International Law (OUP Oxford 2010) at 49–54.

81  General Treaty for the Renunciation of War as an Instrument of National Policy (signed 27 August 1928, entered into force 25 July 1929) 94 LNTS 57.

82  Treaty of Peace between the State of Israel and the Hashemite Kingdom of Jordan (signed 26 October 1994) (1995) 34 ILM 46, art 1.

83  See eg WG Grewe ‘Peace Treaties’ in R Bernhardt (ed) Max Planck Encyclopedia of Public International Law (2nd edn Elsevier Amsterdam 1992–95) vol 3, 938–46 at 943.

84  C Bell On the Law of Peace: Peace Agreements and the Lex Pacificatoria (OUP Oxford 2008).

85  Eg Preliminary Treaty of Peace between Russia and Turkey (signed 19 February 1878) (1878) 152 CTS 395; Treaty between Austria-Hungary, France, Germany, Great Britain, Italy, Russia and Turkey for the Settlement of Affairs in the East (signed 13 July 1878) (1878) 153 CTS 171.

86  C Bell Peace Agreements and Human Rights (OUP Oxford 2000); On the Law of Peace (n 84) 218–58.