Have humans always fought and killed each other, or did they peacefully coexist until states developed? Is war an expression of human nature or an artifact of civilization? Questions about the origin and inherent motivations of warfare have long engaged philosophers, ethicists, anthropologists as they speculate on the nature of human existence. In "How War Began," author Keith F. Otterbein draws on primate behavior research, archaeological research, data gathered from the Human Relations Area Files, and a career spent in research and reflection on war to argue for two separate origins. He...