"The Demon of Unrest" by Erik Larson. A historical account of the events leading up to succession and Civil War, woven around the story of Fort Sumter. I've read other books by Larson and he has a way of making history read a bit more like a novel than dry history without being too simplistic. The introduction compares the historical account of a divided nation to modern times, which seems like an overstatement, but some similarities were there.