To avoid war, one must first understand its causes. Written by two widely respected scholars – both former Presidents of the International Studies Association – this text provides a comprehensive analysis of the leading theories of both interstate war and civil war, along with a discussion of the changing nature of war over time. Utilizing historical examples throughout and adopting a modified “levels–of–analysis” organizational framework, the authors cover systemic, interactional, state and societal level, and decision–making theories of interstate war. These are contrasted with an examination of the conditions and processes leading to civil war. Scholarly and insightful, Causes of War offers a detailed examination of the sources of conflict between and within states and their implications for the future of international relations.