Immanuel Kant famously argued that peace could emerge among states once they shared three features: representative democracy, adherence to international law and organizations, and advanced commercial integration. In the postwar era, these insights guided community-building throughout the developed world. Now Russett and Oneal have provided the most comprehensive statistical analysis of this phenomenon to date. They not only affirm the most debated thesis in world politics -- that democracies virtually never fight each other -- but suggest that democracies are also more peaceful in general than are authoritarian states. They also find evidence that states in highly interdependent economic relationships tend to refrain from fighting with their commercial partners. Furthermore, the more international organizations a state joins, the less likely its government is to use force against other members. The Kantian peace could be seriously undermined by a severe economic downturn, the authors conclude, but no tangible threat exists of a "clash of civilizations." The book does not explain how these complex orders arise in the first place, however.