For an upper level high school student – or for yourself – The Killer Angels by Michael Shaara. What an amazing novel focusing on just a few days during the battle of Gettysburg, from point of view of just a few men on both sides. Won a Pulitzer! And when I finished it, I turned back to the first page and read it straight through all over again.
Also for high school level – An Uncommon Soldier by Lauren Cook Burgess. A collection of actual letters from a soldier who was a girl in disguise as a young man, fighting in the civil war. If Killer Angels looks at a dramatic event, Uncommon Soldier shows the monotonous muddy slog that went on for most of the war, punctuated by a few big battles. Fascinating details of life, though.
I am going to put Uncommon Soldier on my nightstand now that I found it LOL I think I will read it again!