I'm reading Crossroads of Freedom: Antietam
by James M. McPherson. It's a concise history of the events leading up to, during and around the pivotal American Civil War battle. This includes the disasters of the Seven Days Battles, Second Bull Run/Manassas as well as the possibility of British and French intervention in the war.
Whenever I get a spare moment I am also working my way through A Storm of Swords
by George R.R. Martin.