Battle of Antietam

n. Battle of Sharpsburg, bloodiest one-day battle of the American Civil War that took place on September 17th 1862

The Battle of Antietam (also known as the Battle of Sharpsburg, particularly in the South), fought on September 17, 1862, near Sharpsburg, Maryland, and Antietam Creek, as part of the Maryland Campaign, was the first major battle in the American Civil War to take place on Northern soil. It was the bloodiest single-day battle in  American history, with almost 23,000 casualties.
See more at Wikipedia.org...