In this paper, we draw attention to an unintended but severe side effect of just war thinking: the fact that it can impose barriers to making peace. Investigating historical material concerning a series of conflicts in China during the early twentieth century, we suggest that operating in a just war framework might change actors' identities and interests in a way that makes peacemaking an unavailable action. But since just war theory places significant normative constraints on how long wars can be continued, it might thus be self-defeating, in the sense that those who adopt it may undermine the very goals which it is supposed to serve. Whether this finding calls for a revision of existing ethical frameworks governing warfare will depend on whether there are possible alternatives to just war theory that perform better at reining in unjust violence.