Shortly after the Battle of Antietam, President Abraham Lincoln issued the Emancipation Proclamation.

This landmark decision, announced on September 22, 1862, came just days after the battle, which had significant strategic implications for the Union. The proclamation declared that all enslaved people in Confederate-held territory would be set free as of January 1, 1863. This move aimed to weaken the Confederacy’s war effort by undermining its labor force and also reframed the Civil War as a struggle for freedom, thus broadening the Union's objectives and garnering support for the abolitionist cause both domestically and internationally.