Three days later the two armies, led by Lee and McClellan, met again on September 17, 1862, between Antietam Creek and the town of Sharpsburg, Maryland. The Battle of Antietam, also called the Battle of Sharpsburg, was not only the bloodiest day of the American Civil War, it was the single bloodiest day in American history. The Confederate troops took up defensive positions behind Antietam Creek. At this point, McClellan decided to attack.