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Max Planck Encyclopedia of Public International Law [MPEPIL]

Peace Treaties

Jann K Kleffner

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

Armed conflict — Peace treaties — Disarmament — Since World War II — Geneva Conventions 1949 — Belligerence — Prisoners of war

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

A.  Concept and Definition

Peace treaties are agreements concluded between the parties to an armed conflict that end the state of war or the armed conflict between them (Armed Conflict, International). One can broadly distinguish between two types of peace treaties. First, peace treaties stricto sensu are agreements concluded between belligerent States in written form and governed by international law that bring to an end the formal or material state of war between them. Secondly, agreements that are concluded between a non-State party to an armed conflict, on the one hand, and either one or more States or one or more non-State parties, on the other hand, with a view to bringing to an end a non-international armed conflict, are commonly referred to as peace agreements.

B.  Historical Evolution

Peace treaties have a long history. Indeed, due to their intrinsic link to ‘war’ in the non-formal sense and to its termination, peace treaties are a constant in the evolution of international law since ancient times. An important early example is the peace treaty concluded between the Hittite and Egyptian empires after the Battle of Kadesh that took place c 1274 BC. The peace treaty resembled later such treaties in its formal declaration of an end of hostilities and the re-establishment of ‘a good peace and a good fraternity’ among the belligerents. Other precedents stem from ancient Greece, with the Peace of Antalcidas (387 BC) that ended the Corinthian War as a prominent example. Both aforementioned examples also illustrate that peace treaties often go beyond a formal declaration of an end to hostilities and the (re-)establishment of peace, to also set forth the new political order that is held to ensure stability and prevent a relapse into violent conflict. Historically, peace treaties hence recurrently provide important caesura in the development of the regional or global political order. It is this aspect in particular which gives the major peace treaties, including the Westphalian Peace Treaties (Westphalia, Peace of [1648]), their special significance for international relations and law.

While there is a certain degree of continuity between peace treaties of ancient times and those concluded in subsequent periods, a more standardized basic structure of peace treaties evolved in Europe from the late 15th and 16th centuries. That structure remained largely in place until the second half of the 19th century. Standard elements of peace treaties during that period were clauses pledging the willingness to sustain peaceful relations based on the rule of law (amicitia), those regarding amnesty, oblivion, and restitution, and the mutual freeing of prisoners of war (Lesaffer 36, 404; Neff 117–18). These standard elements of the peace treaties of that period were an expression of the evolution of a ius publicum europaeum with the sovereign State at its centre and the ensuing constitutive elements of equality and religious neutrality (Lesaffer 406–9). The European peace treaties of that period did not pronounce on the legality or illegality of the belligerents’ claims in the dispute that gave rise to the resort to the use of force, as illustrated in the practice of leaving each State to bear its own costs of the conflict (Neff 118).

From the late 19th century, the practice of peace treaties began to depart from the dominant features of peace treaties in earlier periods in several respects. First, peace treaties increasingly contained punitive and discriminatory elements. Several such treaties, such as the 1848 Treaty of Guadelupe-Hidalgo between the United States and Mexico (Arts 4, 11 Treaty of Peace, Friendship, Limits, and Settlement [1848] 9 Bevans 791), the Frankfurt Peace Treaty (1871) between France and Germany (‘Traité de paix entre l’Empire Allemand et la France’), and the 1898 Treaty of Paris between the United States and Spain (Arts 2, 3 Treaty of Peace between the United States of America and the Kingdom of Spain [1898] [1896–1899] 30 Stat 1754), provided for territorial concessions of the vanquished State that went well beyond the original causes of the war. In a similar vein, several peace treaties of the second half of the 19th century provided for the payment of indemnities by the vanquished to the victorious State, a practice that, while being contentious at the time, was continued in the Versailles Peace Treaty (1919) and the peace treaties following the Second World War (Neff 211–12; Lesaffer 410).

Secondly, the evolution of legal restraints on the resort to the use of armed force and its gradual outlawing (Use of Force, Prohibition of), with the Kellogg-Briand Pact (1928) and the UN Charter of 1945 as culminating points, meant a revival of the medieval practice rooted in just war doctrine, to distinguish between wrongdoer and victim in relation to waging war. The Versailles Peace Treaty and several of the peace treaties after the Second World War reflected that evolution and were couched in terms of aggressor and victim States and the responsibility of the former (Brownlie 142–45).

Thirdly, due to the evolution of international organizations with a competence in maintaining international peace and security, one can witness a certain diversification of actors in the realm of peace treaties. International organizations gradually came to assume roles in the conclusion of peace treaties between belligerent States as facilitators, mediators or in relation to the implementation of the peace treaty concerned. Indeed, it has been suggested that, on at least one occasion, namely in relation to the Iraq-Kuwait War (1990–91), the UN Security Council has adopted a resolution under Chapter VII of the UN Charter (UNSC Res 687) that effectively served a role similar to that of a peace treaty (Gray 144; contra: Dinstein 53).

C.  Current Legal Situation

1.  Function

The function of peace treaties stricto sensu is, first and foremost, to terminate the ‘state of war’ between the belligerent States and to restore amicable relations between them. According to the ‘state of war doctrine’, the existence of a ‘state of war’ in the formal sense depends on the intention of one or more of the States concerned and commonly commences with a declaration of war. It is not dependent on the actual occurrence of hostilities. Conversely, the States concerned can evade the existence of a state of war in the formal sense by abstaining from making a formal declaration of war, despite the fact that large scale hostilities may occur between them (Brownlie 26; Dinstein 9). However, the importance of the ‘state of war doctrine’ has gradually diminished since the 1920s. The modern law reflects a shift from a subjective notion of what constitutes ‘war’, to the fact-based notion of an international armed conflict. The latter exists when States resort to armed force against one another and renders applicable the pertinent international legal framework (Humanitarian Law, International). This shift is accompanied by several developments in the realm of peace treaties.

First, belligerent States at times use instruments that by substance and form resemble classical peace treaties for the purpose of ending wars in the material sense, ie the actual occurrence of a resort to armed force between States that does not satisfy the requirements for the existence of a state of war in the formal sense between the belligerent parties. A pertinent recent example is the 2000 Agreement between the Government of the Federal Democratic Republic of Ethiopia and the Government of the State of Eritrea. While no declaration of war was made in the instant case (Eritrea-Ethiopia Claims Commission Partial Award Jus Ad Bellum Ethiopia’s Claims 1–8 para 17; Eritrea-Ethiopia Claims Commission), the agreement bears some resemblance to a classical peace treaty in as much as it provides for the permanent termination of military hostilities between the parties, and the repatriation and release of prisoners of war and other detainees, besides other elements, such as an investigation into the root causes of the conflict, and the establishment of a Border Commission and a Claims Commission.

Secondly, much as declarations of war have become the exception and contemporary international armed conflicts between States regularly begin without such formal pronouncements of the actual outbreak of hostilities between States, wars and international armed conflicts are often terminated by less formalized modes than by peace treaties. These modes include implied mutual consent that can be inferred from the mere termination of hostilities; the complete defeat of one of the belligerents (Debellatio) and unilateral declarations (Dinstein 47–50). It has also been suggested that certain instruments which are traditionally regarded as merely suspending hostilities but which do not terminate the state of war or the armed conflict (Suspension of Hostilities), such as armistice[s], have nowadays effectively assumed roles comparable to those of peace treaties (Dinstein 42).

10  In contrast to peace treaties stricto sensu, peace agreements do not have as their function the termination of the ‘state of war’ in the formal sense. This is so because the latter notion is foreign to non-international armed conflicts. The existence of a non-international armed conflict depends on the fact of protracted armed violence between States and organized armed groups or between organized armed groups that are pitted against one another (Prosecutor v Tadić para 70). Conversely, the mere adoption of a peace agreement, while indicating a certain intention of the parties to a non-international armed conflict to end that conflict, does not put an end to the existence of a non-international armed conflict and the applicability of the international legal framework pertaining to it. In that sense, the statement that the law of non-international armed conflict applies ‘until … a peaceful settlement is achieved’ (ibid) only holds true to the extent that the ‘peaceful settlement’ is not a matter of mere agreement, but is also an accurate description of the factual situation on the ground.

11  The functions of peace agreements fall into three broad categories, corresponding each to a particular type of agreement that pertain to a specific stage of a peace process. First, pre-negotiation agreements have the function to regulate who is going to negotiate on behalf of the respective party to the armed conflict and with what status. Secondly, framework or substantive agreements address the substantive issues of the dispute underlying the armed conflict. Thirdly, implementation agreements flesh out the substantive aspects of the framework or substantive agreements (Bell 19–27).

2.  Negotiation and Conclusion

12  The principal actors in negotiating and concluding peace treaties are the parties to the armed conflict in question. However, this does not exclude the participation of third parties. Indeed, the participation of non-belligerents in the negotiation and conclusion of peace treaties has a long tradition, as amply illustrated by the major European peace treaties, including the Westphalian Peace Treaties and the Paris Peace Treaty (1856) (General Treaty for the Re-establishment of Peace [1856] [1855–56] 114 CTS 409). Today, the participation of third States and of inter-governmental and regional organizations is a constant feature of the negotiation and conclusion of peace treaties. The roles assumed by such third parties range from pro-active mediation, such as in the case of the negotiations leading up to the 1995 General Framework Agreement for Peace in Bosnia and Herzegovina ([1995] [1996] 35 ILM 89), to the mere ‘chairmanship’, as was the case with the peace process in Northern Ireland that led to the adoption of the 1998 Good Friday Agreement (Agreement reached in the Multi-Party Negotiations [1998] 37 ILM 751).

13  In the past, it was not uncommon that peace treaties stricto sensu were preceded by peace preliminaries, the main purpose of which consisted in preparing and facilitating a definite peace treaty (Dinstein 39). While such peace preliminaries often bring about an end to hostilities, they do not affect the state of war between the belligerents. Instead, they are merely constitutive of an obligation to reach a peace treaty or to negotiate with a view to reaching such a treaty (Pactum de contrahendo, pactum de negotiando). In the realm of peace agreements, the distinct form of ‘preliminary agreements’ fulfill functions akin to peace preliminaries in as much as they demonstrate the parties’ commitment to conducting future negotiations and reaching a settlement (Definition at UN Peacemaker).

3.  General Features, Content, and Implementation

14  Like other treaties, modern peace treaties commonly begin with a preamble, which sets forth the general context, the broad object and purpose of the treaty in question, and regularly contains the expression of the parties’ desire to establish a sustainable peace between them, as well as a pledge to settle future disputes by peaceful means (Peaceful Settlement of International Disputes). The preamble is usually followed by an opening operative provision, in which the parties declare that the state of war or the armed conflict between them shall be terminated. In addition, peace treaties stricto sensu regularly contain clauses that provide for the restoration of friendly relations between the belligerent states. The precise content of the subsequent operative provisions of peace treaties depends on the issues that underlie the armed conflict in question. However, notwithstanding the idiosyncracies of a given conflict, one can identify some broad categories of issues that the operative provisions of peace treaties regularly address. These issues only partially overlap with those that featured in classical peace treaties. The evolution of international law to regulate matters such as the use of force, human rights, refugees, and internally displaced persons, as well as the close interplay between international and domestic legal issues in non-international armed conflicts, have brought about a departure from the fairly rigid scheme governing the content of traditional peace treaties that had developed since the Middle Ages (see above para. 3). The Versailles Peace Treaty constitutes an important reflection of the shift from classical to modern peace treaties.

15  A first category of provisions that modern peace treaties commonly contain consists of those that address the consequences of the conflict. Typical provisions in that regard pertain to matters such as prisoners of war and other conflict-related detainees (eg Art. 2 (1) and (2) Agreement between the Government of the State of Eritrea and the Government of the Federal Democratic Republic of Ethiopia; Arts IXXI Peace Agreement between the Government of Liberia, the Liberians United for Reconciliation and Democracy, the Movement for Democracy in Liberia and the Political Parties). Provisions on the release of prisoners of war and other conflict-related detainees are without prejudice to the applicable rules of the law of armed conflict that may oblige parties to an armed conflict to release them prior to the conclusion of a peace treaty. More in particular, prisoners of war must be released and repatriated without delay after the cessation of active hostilities (Art. 118 Geneva Convention relative to the Treatment of Prisoners of War), civilian internees must be released as soon as the reasons which necessitated the internment no longer exist (Art. 132 Geneva Convention relative to the Protection of Civilian Persons in Time of War). Other typical provisions that address the consequences of the conflict relate to displaced persons (eg Arts 1920 Agreement on a Comprehensive Political Settlement of the Cambodia Conflict; Arts 12, 13, and 20 (1) (a) Pact on Security, Stability and Development in the Great Lakes Region).

16  A second category of provisions addresses measures that are taken to avoid a relapse into armed conflict. Peace treaties that are being adopted after an international armed conflict over territory commonly contain clauses that regulate the peaceful settlement of the underlying territorial dispute (eg Art. 4 Agreement between the Government of the State of Eritrea and the Government of the Federal Democratic Republic of Ethiopia). In peace agreements, provisions typically address matters such as the disarmament, demobilization, rehabilitation, and reintegration of members of the armed forces of organized armed groups, restructuring and training of governmental armed forces, democratization and power-sharing, and human rights issues (eg Arts IIIVIII, XVI, XVII, and XXIVXXVI Peace Agreement Between the Government of Sierra Leone and the Revolutionary United Front of Sierra Leone [‘Lomé Agreement’]). Amnesty clauses are also a recurring feature of peace agreements (eg Art. IX Lomé Agreement; Art. XXXIV Peace Agreement between the Government of Liberia, the Liberians United for Reconciliation and Democracy, the Movement for Democracy in Liberia and the Political Parties), notwithstanding the controversies surrounding amnesty for international crimes, such as genocide, crimes against humanity, and war crimes that may have been committed during the armed conflict in question.

17  Provisions that address the procedural and institutional dimensions of the implementation of, and monitoring over the compliance with, the terms of the peace treaty constitute a third category. These dimensions can range from the setting up of, and the procedures applicable to, joint commissions (eg Arts IV and IV Appendix to Annex I Treaty of Peace between the Arab Republic of Egypt and the State of Israel), bodies entrusted with investigating the causes of the conflict (Art. 3 Peace Agreement between the Government of the State of Eritrea and the Government of the Federal Democratic Republic of Ethiopia) and boundary commissions in the case of territorial disputes (ibid Art. 4) to mixed claims commissions (ibid Art. 5) and the role of third parties, such as inter-governmental and regional organizations and third States in implementation and monitoring (eg Arts XIII–XVI Lomé Agreement). A recurring feature of peace agreements is the establishment of transitional bodies, including transitional governments (eg Art. XXI Peace Agreement between the Government of Liberia, the Liberians United for Reconciliation and Democracy, the Movement for Democracy in Liberia and the Political Parties) and transitional justice mechanisms, such as truth and reconciliation commissions (eg Art. XXVI Lomé Agreement; Art. XIII Peace Agreement between the Government of Liberia, the Liberians United for Reconciliation and Democracy, the Movement for Democracy in Liberia and the Political Parties). At times, matters concerning the implementation and monitoring of peace treaties such as the aforementioned ones are subject to separate regulation in implementation agreements (Bell 27–29; UN Peacemaker).

D.  Special Problems

1.  Applicability of the General Law of Treaties to Peace Treaties Stricto Sensu

18  As written international agreements are concluded between States and governed by international law, the conclusion, entry into force, observance, application, and interpretation, as well as other matters, such as the modification and amendment of peace treaties stricto sensu are governed by the applicable lex generalis as stipulated in the Vienna Convention on the Law of Treaties (1969) (‘VCLT’). However, given the nature of peace treaties stricto sensu, the following specific provisions of the VCLT deserve particular mention.

19  First, according to Art. 52 VCLT, a treaty is void if its conclusion has been procured by the threat or use of force in violation of the UN Charter (Treaties, Validity). In other words, provisions of a peace treaty that are imposed by an aggressor State on a victim of aggression have no legal force (Art. 69 (1) VCLT). Art. 52 VCLT has crystallized into a norm of customary international law (see Fisheries Jurisdiction Case [Federal Republic of Germany v Iceland] [Jurisdiction of the Court] para. 24). The invalidity that is the consequence of the threat or use of force in violation of the UN Charter affects the peace treaty in its entirety (Art. 44 (5) VCLT). However, the nullity of such a peace treaty does not affect the duty of any State to fulfill any obligation embodied in the treaty to which it would be subject under international law independently of the treaty (Art. 43 VCLT). One such obligation is to refrain from using force in violation of the UN Charter and the corresponding rule of customary international law. In other words, the invalidity of the peace treaty by virtue of Art. 52 VCLT leaves unaltered the prohibition of the use of force. The nullity of the peace treaty hence does not reinstate the state of war between the former belligerents (Dinstein 41). Art. 43 VCLT applies not only in the context of the invalidity of treaties, but also in the context of their termination or denunciation (Treaties, Termination), the withdrawal of parties from them, or the suspension of their operation. Accordingly, a material breach of a peace treaty stricto sensu does not entitle the other party to terminate the treaty and resume hostilities, notwithstanding that Art. 59 VCLT provides that ‘[a] material breach of a bilateral treaty by one of the parties entitles the other to invoke the breach as a ground for terminating the treaty or suspending its operation in whole or in part’. Under the current law, such material breach hence cannot provide a legal basis for the assertion that provisions of a peace treaty can be enforced by the use of armed force (for analysis of that argument prior to the adoption of the VCLT, see Brownlie 342–4.)

20  Secondly, as a normative complement to Art. 52 VCLT, Art. 75 VCLT stipulates that the VCLT is without prejudice to any obligation in relation to a treaty which may arise for an aggressor State in consequence of measures taken in conformity with the UN Charter with reference to that State’s aggression. The provision hence contemplates and condones that a State which has been the victim of aggression imposes upon the aggressor State a peace treaty in the course of exercising its right to self-defence.

2.  Legal Status of Peace Agreements

21  Due to the fact that non-State organized armed groups are parties to them, peace agreements are not subject to the 1969 VCLT (Arts 1 (1) in conjunction with 2 (1) (a) VLCT) and the 1986 Vienna Convention on the Law of Treaties between States and International Organizations or between International Organizations (‘VCLT-IO’) (Art.1 VCLT-IO). However, as is clear from both Vienna Conventions, the exclusion of other instruments from their regulatory ambit is without prejudice to any legal force that such other instruments may possess (Arts 3 (a) VLCT and VCLT-IO). While the two Vienna Conventions on the Law of Treaties clearly contemplate the existence of international agreements other than those concluded between States or between States and international organizations or between international organizations, the international legal status or lack thereof of peace agreements is uncertain.

22  The drafting history of the 1986 VCLT-IO suggests that the International Law Commission (ILC) was of the view that the extension of the law of armed conflict to ‘entities which have not yet been constituted as States’ means that agreements to which such entities are parties are agreements governed by international law (UN ILC ‘Draft Articles on Treaties Concluded Between States and International Organizations or Between International Organizations’ 125). The Commission hence seems to have regarded the fact that organized armed groups are subject to the law of armed conflict, and notably the law applicable in non-international armed conflicts as granting them international legal personality and treaty-making capacity.

23  In contrast, when the Special Court for Sierra Leone was confronted with the question of whether the Lomé Agreement created obligations under international law for the parties to it, the Court answered in the negative (Prosecutor v Kallon). It argued that the fact that organized armed groups are subject to the law of armed conflict does not automatically entail their being granted international legal personality (ibid para. 45) and that the signatory organized armed group in question, the Revolutionary United Front, lacked treaty-making capacity (ibid paras 46–50). Indeed, the Court’s argumentation suggests that it viewed all organized armed groups as lacking that capacity, although the Court acknowledged the possibility that a peace agreement may create rights and obligations under domestic law (ibid para. 49).

24  It is submitted that to determine the question of the status under international law of peace agreements from the perspective of international legal personality is of little assistance. This is so because of the circular nature of determining that personality. It is commonly held that an international legal person is an entity that possesses rights and obligations under international law (Reparation for Injuries Suffered in the Service of the United Nations [Advisory Opinion] 8–9), while the determination of whether such rights and obligations exist draws on whether the addressee of those rights and obligations possesses international legal personality. A better way of determining whether a peace agreement is governed by international law is to examine the intention of the parties to the agreement. Absent clear statements of the parties to that effect, the context in which the agreement has been concluded is relevant in determining that intention (see mutatis mutandis Oppenheim 1202). It has been suggested, for instance, that the significant involvement by the parties to an armed conflict of intergovernmental organizations, and in particular the UN, in the conclusion of a peace agreement, may be indicative of the intention of the signatories to adopt a peace agreement that is international in character (Kooijmans 338).

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