Berlin persistently wrote about slavery’s varied effects across the years, but he never lost sight of the cruelty. “In books like Slaves Without Masters: The Free Negro in the Antebellum South (1974) and Many Thousands Gone: The First Two Centuries of Slavery in North America (1998), Dr. Berlin, a longtime professor at the University of Maryland, upended simplistic notions of how slavery was practiced and what happened after it ended.”