The Killer Angels is historical fiction because it's… fiction… about history. No great mystery there. And on a similar note, it's a war drama, because it's… a drama… about war.
But The Killer Angels isn't the kind of historical fiction that deals with sad royal childhoods or a young milkmaid who falls in love with a sexy pirate. This is hardcore history—detailed descriptions of warfare… with maps, even. Lots of maps. Abraham Lincoln: Vampire Hunter it ain't. You don't need to love in-depth descriptions of strategy to really vibe with this baby—but it definitely helps.