This course explores the causes of modern war with a focus on preventable causes. Course readings cover theoretical, historical, and methodological topics. Major theories of war are explored and assessed in the first few weeks of the class, asking at each stage "are these good theories?" and "how could they be tested?" Basic social scientific inference -- what are theories? What are good theories? How should theories be framed and tested? -- and case study methodology are also discussed. The second half of the course explores the history of the outbreak of some major wars. We use these cases as raw material for case studies, asking "if these episodes were the subject of case studies, how should those studies be performed, and what could be learned from them?"