In this major study of the causes of war, David Welch argues that, contrary to the received wisdom in academic and policy circles, states are often motivated by sincere concern for the perceived demands of justice, not merely by self interest. By examining the outbreak of five Great Power wars (the Crimean War, the Franco-Prussian War, World War I, World War II, and the Falklands War), Welch demonstrates the importance of the justice motive in state behavior, using both historical and philosophical analysis to shed new light on an old problem.