Its amazing to think that the tragic number of deaths on September 11, 2001 is still over a 1000 deaths less than the number who died on September 17, 1862. There were also several thousand soldiers who died from their wounds in the days following the Battle of Antietam as well. It was significant not just for the amazing number of casualties, but also because it was the Confederate Army's first campaign across the Potomac. Although Gettysburg is remembered as a clear defeat of the Confederates by the Union army, Antietam was more of a draw. Each side suffered great casualites, and while the Confederates had to cross back to Virginia, the Union failed to run after Lee and his army, and engage them during their retreat. So while there was no clear victory for the Union army, the Battle of Antietam hurt the South because of their lack of success while invading Union territory.