The Killer Angels. The book is a slightly fictionalized account of the Battle of Gettysburg which began June 30, 1863. One of my favorite books of all-time and a I book I think every high school senior should required to read.
Once done with The Killer Angels next up with be Michael Herr's classic Dispatches. Normally I don't read books I have already read back-to-back but with the passing of Michael Herr I feel the need to make an exception. Even if you haven't read Dispatches you may be familiar with Herr's work as one of the screenwriters of Full Metal Jacket.