In the spring of 1955, a graduate student at Harvard met a visiting professor from Berkeley. Their encounter helped to change how history is written, and slavery’s place in that story.

The student was David Brion Davis, then 28, whose experiences in America’s segregated Army had sensitized him to the country’s racial problems. The professor was Kenneth M. Stampp, then 44, who was about to publish The Peculiar Institution, the first major challenge to the racist slavery scholarship that prevailed at the time.

Stampp’s example taught Davis the urgent need to re-examine the then-marginalized subject of slavery. That became his life’s work. It culminates this month when Knopf publishes The Problem of Slavery in the Age of Emancipation, the final book in a trilogy that Davis, who is about to turn 87, began more than 50 years ago....