Realism has dominated international relations theory at least since World War II. 1 For realists, international anarchy fosters competition and conflict among states and inhibits their willingness to cooperate even when they share common interests. Realist theory also argues that international institutions are unable to mitigate anarchy’s constraining effects on inter-state cooperation. Realism, then, presents a pessimistic analysis of the prospects for international cooperation and of the capabilities of international institutions. 2