The Battle of Antietam was the 1862 battle that became the bloodiest single-day battle in American history.
Fought on September 17, 1862, near Sharpsburg, Maryland, Antietam pitted General Robert E. Lee's Army of Northern Virginia against Major General George B. McClellan's Army of the Potomac. Lee had invaded Maryland after the Confederate victory at Second Bull Run, hoping to shift the war northward and encourage foreign recognition of the Confederacy.
The fighting unfolded across places that became synonymous with Civil War carnage: the Cornfield, Dunker Church, the Sunken Road—later called Bloody Lane—and Burnside Bridge. Repeated attacks and counterattacks produced roughly 22,700 combined Union and Confederate casualties in a single day.
Antietam was not a decisive battlefield victory for the Union, but Lee withdrew to Virginia afterward. That retreat gave President Abraham Lincoln the opportunity to issue the preliminary Emancipation Proclamation, making the battle a major political and strategic turning point. It is also called the Battle of Sharpsburg, especially in the South.