As I noted in s.1.4, the oldest surviving peace treaty was concluded in c.1259 bc. Since then, peace treaties, or agreements, have become a staple of international diplomacy. They are also increasingly used, not merely to carve out territory amongst belligerents but rather to provide a multipronged framework for rebuilding communities shattered by war. Inter alia, they act as constitutional settlements, set out conditions for reparations and reconstruction, provide for the prosecution of major war criminals and the amnesties of small (and not so small) fry, and set out guidelines for the return of refugees.1
By their very nature, treaties generate special rights and duties between signatories the exercise and fulfilment of which is inherently exclusionary. Cosmopolitans are wary of special relationships based on communal membership in so far as those relationships are exclusionary vis-a-vis outsiders, and they should thus be particularly concerned with treaties precisely for that reason. And yet, they have not paid attention to those kinds of special relationships. Nor have war ethicists spent much time on this issue.2 A cosmopolitan theory of the jus post bellum must provide an account of the grounds upon and conditions under which such treaties can be binding on their parties, and of the degree to which treaty obligations supersede, or are outweighed by, those parties’ general obligations to outsiders.
In the course of this and the next five chapters, I argue that an agreement, or treaty, is binding on its parties if and only if it meets the following two conditions: (1) a procedural condition, whereby (1a) the agreement is not secured by fraud, deception, or unjustified coercion, and (1b) parties who negotiate the agreement are properly empowered to do so; (2) a substantive condition, whereby the agreement’s clauses (2a) are at the very least justifiedATC vis-a-vis its parties and (2b) do not prevent the latter from meeting their overriding obligations of justice to outsiders. My aim in this chapter is twofold: to provide a justification for the claim  
that parties to a peace treaty are under an obligation to comply with its provisions, and to articulate and defend the procedural condition. In subsequent chapters, I offer a detailed account of the substantive condition.
I proceed as follows. In s.4.2, I claim that peace agreements fulfil a number of different functions and I provide a justification for the duty to comply which takes those functions into account. Having thus shown that, and why, parties are under a duty to meet their treaty obligations, I argue in s.4.3 that the moral status of the war has a bearing on the procedural justness, or lack thereof, of a peace treaty, and by implication on its bindingness.
Before I start, however, a definitional caveat is in order. As Christine Bell notes in her comprehensive study of contemporary practice, as a matter of fact, peace treaties, or peace agreements (I shall use the terms interchangeably), range from pre-negotiations undertakings (for example, to agree on a ceasefire), to substantive frameworks for institution-building and reconstruction. They also comprise agreements to implement the latter. Moreover, again as a matter of fact, they have been used to put an end to relatively small-scale conflicts in which a few thousand people have died, as well as to large-scale conflicts characterized by genocidal campaigns. They have been concluded between sovereign states, between rulers of empires and kingdoms vastly different in form and status from modern nation states, between factions within states, between states and so-called indigenous actors, and/or in intra-state cases under the auspices of international organizations or other states. Faced with this bewildering diversity of practices and documentary and legal diversity spanning several thousand years, it is crucial to adopt a working definition which makes sense of the notion of peace agreement in general. I draw on and revise Christine Bell’s definition, to the effect that ‘peace agreements are documents produced after discussion with some or all of the conflict’s protagonists, that address militarily violent conflict with a view to ending it’, and whose constitutive clauses solely set out parties’ rights and duties.
-  The UN maintains a database of over 800 peace agreements—related documents at http://peace-maker.un.org/ For a useful and concise study of contemporary peace agreements, see J. S. Easterday,‘Peace Agreements as a Framework for Jus Post Bellum , in J. S. Easterday, J. Iverson and C. Stahn (ed.),Jus Post Bellum (Oxford: Oxford University Press, 2014). For a comprehensive treatment, see C. Bell,On the Law of Peace: Peace Agreements and the Lex Pacificatoria (Oxford: Oxford University Press,2008). I shall use the words ‘treaty’ and ‘agreement’ interchangeably.
-  For a notable exception, see D. Schwartz, ‘The Justice of Peace Treaties’, The Journal of PoliticalPhilosophy 20 (2012): 273-92.
-  Bell, On the Law of Peace, 53. Chs. 2 and 3 of that book offer an illuminating account of thediversity of peace agreements and a fascinating recounting of their history. As an anonymous refereefor Oxford University Press pointed out to me, Bell’s definition as it stands will not do, since it countsa formal document containing a threat to resume war as a peace agreement, so long as the threat isintended to stop war. Hence my adding the proposition ‘and whose constitutive clauses . . .’