The onset, expansion and consequences of inter-state conflict lie at the heart of international relations scholarship. This class will explore these topics, highlighting what we know and what we do not know. We will start by clarifying our concepts and what we mean when we use terms like “dispute” and “war.” Then, we will examine the inadequacy of the conventional wisdom in international relations that purports to explain war and peace by reference to structural properties of the international system. Next, we discuss theories and research programs that eschew structural properties in favor of either the properties of states or the issues that make them susceptible to fight each other. We will conclude the class with a discussion of some methodological and theoretical issues to help unify our approach to the study of international conflict. These discussions include the importance of bargaining, research design, and selection effects to the study of international conflict. Students that complete this class should have a broad overview of prominent scholarship on the cause of disputes and war in the international system.