Factual error: When Shaw tells a reporter how well his men did in battle, in the background you can the southern tune "The Bonnie Blue Flag with the Single Star" playing. It's a southern anthem, so wouldn't be played in a Union camp.
Continuity mistake: When Colonels Shaw and Montgomery are in Darien, Georgia, Montgomery shoots a soldier (apparently in the heart) for touching a white woman. When the troops are marching out of the town, the soldier who was shot has miraculously felt better, gotten back up and joined the ranks. (01:07:05 - 01:08:55)
Answer: The Battle of Antietam, also known as the Battle of Sharpsburg. It took place 9/17/1862. 3,675 men lost their lives, with an additional 17,301 wounded that day.
Bishop73