The neorealist-neoliberal debate about the possibilities for collective action in international relations has been based on a shared commitment to Mancur Olson's rationalist definition of the problem as one of getting exogenously given egoists to cooperate. Treating this assumption as a de facto hypothesis about world politics, I articulate the rival claim that interaction at the systemic level changes state identities and interests. The causes of state egoism do not justify always treating it as given. Insights from critical international relations and integration theories suggest how collective identity among states could emerge endogenously at the systemic level. Such a process would generate cooperation that neither neorealists nor neoliberals expect and help transform systemic anarchy into an “international state”—a transnational structure of political authority that might undermine territorial democracy. I show how broadening systemic theory beyond rationalist concerns can help it to explain structural change in world politics.