Leon F. Litwack, a Pulitzer Prize-winning historian who illuminated dark corners of the American past by exploring the bitter legacy of slavery and segregation and by confronting the lingering presence of white supremacy in the national consciousness, died Aug. 5 at his home in Berkeley, Calif. He was 91.

The death was confirmed by his wife, Rhoda Litwack. The cause was bladder cancer.

Dr. Litwack spent most of his academic career at the University of California at Berkeley, where he taught an introductory survey of American history that routinely attracted more than 700 students a semester.

He was the author of several landmark works, including “Been in the Storm So Long: The Aftermath of Slavery” (1979), which won the Pulitzer Prize, the National Book Award and the Francis Parkman Prize for history. Historian Nell Irvin Painter called the book “an intricate, vivid mosaic of Emancipation as experienced on both sides of the color line.”

Dr. Litwack was “the first historian to make use, in a general work on the Reconstruction era, of the thousands of slave narratives collected by interviewers from the Federal Writers’ Project during the New Deal,” historian David Herbert Donald noted in the New Republic. The result, Donald added, was “a long book, an important book, and a richly rewarding book [that] belongs on that short shelf of indispensable works on Southern history.”

With his emphasis on history from the ground up, Dr. Litwack can be seen in some respects as an intellectual forebear of recent movements to focus attention on the country’s racial divide and the plight of marginalized groups in American life.

“Few people have cared more deeply about this nation than some of its severest critics,” Dr. Litwack told Historymatters.com website in 2001, “and . . . we need to be wary of those who in the name of protecting our freedoms would diminish them. History teaches, after all, that it is not the rebels, the iconoclasts, the curious, the dissidents who endanger a democratic society but rather the accepting, the unthinking, the unquestioning, the docile, the obedient, the silent, and the indifferent.”