International law has long been burdened with the charge that it is not really law. This misleading claim is premised on some undeniable but misunderstood facts about international law: that it lacks a centralized or effective legislature, executive, or judiciary; that it favors powerful over weak states; that it often simply mirrors extant international behavior; and that it is sometimes violated with impunity. International law scholarship, dominated for decades by an improbable combination of doctrinalism and idealism, has done little to account for these characteristics of international law. And it has made little progress in explaining how international law works in practice: how it originates and changes; how it affects behavior among very differently endowed states; when and why states act consistently with it; and why it plays such an important role in the rhetoric of international relations.
This book seeks to answer these and many other related questions. It seeks to explain how international law works by integrating the study of international law with the realities of international politics. Our theory gives pride of place to two elements of international politics usually neglected or discounted by international law scholars: state power and state interest. And it uses a methodological tool infrequently used in international law scholarship, rational choice theory, to analyze these factors. Put briefly, our theory is that international law emerges from states acting rationally to maximize their interests, given their perceptions of the interests of other states and the distribution of state power. We are not the first to invoke the idea of state interest to explain the rules of international law (Oppenheim 1912). But too often this idea is invoked in a vague and conclusory fashion. Our aim is to integrate the notion of state interest with simple rational choice models in order to