A Pulitzer Prize-winning historian and author, he is best known for his work on post-Civil War Reconstruction. He published his award-winning work, The Fiery Trial: Abraham Lincoln and American Slavery, in 2010.
He graduated summa cum laude from Columbia University in 1963.
He was elected president of the American Historical Association in 2000.
His father was a historian who was blacklisted during the McCarthy Era for supporting civil rights and the trade union movement.
He frequently wrote about Abraham Lincoln's views on slavery.