The significance of the Battle of Antietam lies in its status as the bloodiest single-day battle in American history, with approximately 22,000 casualties on both sides.

Fought on September 17, 1862, it marked a crucial turning point in the Civil War. The battle halted General Robert E. Lee’s invasion of the North and provided the Union with a strategic advantage. Following the battle, President Abraham Lincoln issued the Emancipation Proclamation, which aimed to free enslaved people in Confederate states. This shifted the war's focus to include the moral imperative of abolition, fundamentally redefining its purpose.