Why Do Nations Obey International Law?

Why do nations obey international law? This remains among the most perplexing questions in international relations. Nearly three decades ago, Louis Henkin asserted that "almost all nations observe almost all principles of international law and almost all of their obligations almost all of the time."' Although empirical work since then seems largely to have confirmed this hedged but optimistic description, scholars have generally avoided the causal question: If transnational actors do generally obey international law, why do they obey it, and why do they sometimes disobey it?