Justice is important, but so is peaceful cooperation. In this article, I argue that if one takes seriously the autonomy of individuals and groups and the fact of moral pluralism, a just system of cooperation cannot guarantee peaceful cooperation in a pluralistic world. As a response to this consideration, I develop a contractarian theory that can secure peace in a pluralistic world of autonomous agents, assuming that the agents who exist in this world expect that peaceful cooperation is the most (...) beneficial form of interaction for them in the long run. The theory specifies the restrictions on the behavior of autonomous individual and collective agents that are indispensable for peaceful cooperation in a pluralistic world. In particular, I argue for the need of (i) a globally valid rule of conflict resolution to settle all intra- and inter-group conflicts that cannot be resolved locally, (ii) a world court to apply this rule in cases where local group authorities are inadequate to do so, and to serve as a final court of appeal, and (iii) a world police to enforce the rule. (shrink)