Combining a detailed examination of theory with a full and up-to-date account of historical development, this study analyzes the nature of the international order—the hierarchical state system—and explores its potential for reform. The theoretical account is given tracing two traditions of thought in the writings of Kant and Rousseau, while the historical survey explores the evolution of international organizations since 1815, covering such aspects as concert diplomacy, alliance systems, international organizations, and such internal understandings as nuclear deterrence, crisis management, and sphere of influence. The Hierarchy of States succeeds and replaces Clark's Reform and Resistance in the International Order (CUP, 1980).