He started out writing for newspapers. After serving during WWII as director of information for the U.S. War Production Board, he wrote his first book, about war-time Washington. He became a full-time writer, focusing on the American Civil War.
He won the Pulitzer Prize in history for A Stillness at Appomattox, although he had no formal training in history.
[on his passion for writing about the Civil War] When I was growing up in northern Michigan, all the old men in town were Civil War veterans. We boys used to sit around and listen to their yarns and see them parading in Fourth of July celebrations. There was one old fellow who used to beat his army drum at dusk on summer evenings. I grew up surrounded by the traditions of that war, and I suppose I always had the desire to write about it in the back of my mind.