General James Longstreet at Antietam: Longstreet’s Account of the Battle from His Memoirs, From Manassas to Appomattox

One of the most important Confederate generals of the Civil War was Lieutenant General James Longstreet, the man Robert E. Lee called his “old war horse.” Longstreet was arguably the best corps commander the Confederates have, and he played crucial roles at Antietam, Second Bull Run, Chickamauga, the Wilderness, and Fredericksburg. However, Longstreet had a controversial role at Gettysburg, when he was unable to roll up the Union Army of the Potomac's flank on Day 2 and Pickett's Charge failed on Day 3. Though Longstreet tried to talk Lee out of the attacks, they went forward, and Longstreet criticized Lee about them afterward, making him reviled among other Confederates. In turn, they tried to blame him for the loss at Gettysburg.  
Just a few years before his death, Longstreet finally published his crucial memoirs, From Manassas to Appomattox, which talked about his experiences and analysis of the decisions made during the war. Longstreet wrote it to respond to his own critics and because Lee himself didn't write any. Regardless, they are one of the most important post-war writings of any general on either side of the Civil War.