Ordinary Men (1992)

The book that best answers the question readers ask after their first memoir: how did ordinary people become mass murderers? Christopher Browning studied Reserve Police Battalion 101, a unit of about 500 German Order Police who shot and rounded up Jews in occupied Poland in 1942, including in the massacres at Józefów and Łomazy. Their commander once offered the men the chance to opt out. Fewer than a dozen took it. Drawing on the men's own postwar testimony, Browning refuses the comfort of calling them monsters, and that is what makes the book so unsettling. Short and sober, it is the one history on this list every teacher of the subject should read.