The effect of Antietam on Lincoln's policies was that he pushed for emancipation.

The outcome of the battle, viewed as a strategic triumph, gave Lincoln the leverage he needed to issue the Emancipation Proclamation. This decision not only sought to undermine the Confederacy by liberating enslaved individuals in rebel states but also redefined the war's objective, presenting it as a moral fight against slavery. The proclamation invigorated abolitionist sentiment in the North and aimed to deter foreign nations from supporting the Confederacy, marking a pivotal moment in U.S. history.