The Battle of Antietam, fought on September 17, 1862, is the deadliest single-day battle in American history, with around 23,000 casualties.

Although it ended in a tactical stalemate, it was a strategic victory for the Union because it halted Confederate General Robert E. Lee's invasion of the North. This battle provided President Abraham Lincoln with the opportunity to issue the Emancipation Proclamation, redefining the war's purpose to include the fight against slavery. Antietam thus became a crucial turning point in the Civil War