On this day, September 17, 1862, 23,000 men died or were wounded in the Battle of Antietam, Maryland.
… it was also the bloodiest single day battle in American history …
… Antietam resulted in nine times as many Americans killed or wounded (23,000 soldiers) as took place on June 6, 1944–D-day, the so-called “longest day” of World War II.* Also consider that more soldiers were killed and wounded at the Battle of Antietam than the deaths of all Americans in the Revolutionary War, War of 1812, Mexican War, and Spanish-American War combined.
The victory by the north provided Lincoln with the occasion he needed to announce the abolition of slavery in the South.