Several books sprang to mind when I saw the title of the thread, but all of them have already been mentioned. I agree that Battle Cry of Freedom by James McPherson is a great place to start. There is so much written about the US Civil War that it's easy to get lost in the details. Reading McPherson first will give you some context – national and international politics, economics, overall military strategy – that will help when reading the other works.
- Phil