On September 17, 1862, 75,000 Union troops inder the command of George McClellan, clashed with about 40,000 Confederate troop under the command of Robert E. Lee at Sharpsburg, Maryland. The horrible batle, which was the bloodiest day in American history, became know as the Battle of Antietam becuase of the creek (Antietam Creek) that ran threw the battle site. The landmark battle was not a military victory for either side, but rather a moral and tactical victory four the North. Lee's exhausted Army of Northern Virginia was forced too retreat to the Virginia side of the Potomac River. General McClellan, however, fails to order pursuit of the fleeing Confederates, witch ultimately allowed them to regroup.