Studies of the relationship between the distribution of power and prospects for conflict or cooperation have a distinguished history in the field of international politics. Several competing theories have been offered to explain variation in foreign policy behavior as a function of power distributions. Moreover, a wealth of empirical evidence suggests the crucial role that power plays in international bargaining. The Origins of Major War is a deeply penetrat- ing, extraordinarily wide-ranging, and judicious treatment of the onset of major conflict, and it offers an explanation and some evidence for the relationship between power differentials and major power conflict. Copeland provides a dynamic theory of major power war, building upon classic realism. In my view, his diagnosis and combination of prescription are substantially correct.