What excatly is the Antietam battle

Antietam, Battle of Antietam Creek, near the village of Sharpsburg, Maryland, was the scene of a famous battle in the Civil War, when the states of the North and those of the South fought against each other from 1861 to 1865. The Battle of Antietam, on September 17, 1862, was between Northern troops under General G. B. McClellan and a Southern army commanded by General Robert E. Lee.

Although McClellan had a far larger army, he was unable to drive back Lee's troops, who held their lines all during the day in the bloodiest and most terrible battle that had been fought in the war. After the shooting stopped for the day, Lee quietly withdrew his troops and marched back into the state of Virginia. McClellan might have followed him immediately and continued the battle, but did not. The Battle of Antietam was Lee's first invasion of Northern territory, and while he was not defeated in battle, this attempt to invade the North was a failure