What Was the Cause of the Battle of Antietam?

The Battle of Antietam during the American Civil War was caused by General Robert E. Lee's desire to follow up his victory at the second Battle of Manassas by heading north into Maryland. His intentions were to sever rail links to Washington and seize supplies. When Union Major General George B. McClellan learned of Lee's plan, he moved to intercept him.

The Battle of Antietam was the first battle of the Civil War fought on northern soil. Though he had the advantage due to the copy of Lee's plan that reached his hands, McClellan moved too slowly to take full advantage of it. Lee had the Potomac River at his back and only one escape route, and his men were scattered in several units. McClellan's delay allowed Lee to consolidate his army. On Sept. 17, 1862, the battle began. After indecisive fighting in an area called Miller's Cornfield, Union troops attacked Lee's center in a place afterward referred to as Bloody Lane. Throughout the battle, McClellan, believing that Lee possessed many more troops than he did, refused to commit his reserve forces to the fight.

The Battle of Antietam was the bloodiest day in American military history. On the Union side, casualties included more than 2,100 killed, 9,500 wounded and 750 missing or captured. The Confederate count was more than 1,500 killed, 7,700 wounded and 1,000 missing or captured. Though the battle ended inconclusively, Lee crossed the Potomac and headed back into Virginia. President Abraham Lincoln, claiming a strategic victory, used the occasion to issue the Emancipation Proclamation, which freed all the nation's slaves.