Donald Kagan (1932 - 2021), who passed away this summer, was a preeminent historian of both the ancient and modern worlds. In 2015, we were privileged to host Professor Kagan for a wide-ranging Conversation about the major themes of his work. We are pleased to re-release the Conversation here. In the Conversation, Kagan and Kristol discuss what humanity's greatest wars—from the Peloponnesian War to World War II—can teach us about the nature of war and the sources of human conflict. Kagan also discusses his education in history at Brooklyn College, his groundbreaking work on Thucydides, and his distinguished teaching career at Yale. Finally, Kristol and Kagan discuss the state of the study of history and the liberal arts more generally in America.