The Battle of Antietam was fought on September 17, 1862. The location was near Sharpsburg, Maryland. Because of this, the second name for this battle is the Battle of Sharpsburg. The Battle of Antietam is the first battle in the American Civil War to take place on Union territory. Also, this is the deadliest battle in American history, with 22.717 people killed, wounded or missing.
Major General George B. McClellan launched an attack on an army of the Confederate General Robert E. Lee. The attack was launched in a defensive position. The battle started at dawn, when Maj. Gen. Joseph Hooker launched an assault on the left flank of Lee’s forces. The fighting swirled around the Dunker Church. In the afternoon, forces of the Maj. Gen. Ambrose Burnside entered into the battle. They captured the stone bridge over the Antietam Creek. Later that day, Maj. Gen. A. P. Hill's forces arrived from Harpers Ferry and started a counterattack. They ended the battle.
George B. McClellan had at his disposal, 75.500 soldiers. 2.108 of them were killed, 9.540 were wounded and 753 were captured or missing, making the total number of 12.401. On the other side, Robert E. Lee had 38.000 soldiers. 1.546 were killed, 7.752 were wounded and 1.018 were captured or missing, making the total number of 10.316.
McClellan's attack was unsuccessful because it failed to achieve force concentration. As the result, McClellan failed to defeat the Lee’s forces. He was able to move his army to Virginia. The outcome of the battle is officially inconclusive, but because Confederate troops left the battlefield first, in military terms, this is a Union victory.