The battle had a significant impact on British policy towards the war. Before Antietam, the British government had been considering recognizing the Confederacy as an independent nation. However, the Union victory at Antietam convinced them that the Confederacy was unlikely to win the war, and they decided to maintain their neutrality.
In addition, the Emancipation Proclamation, which President Lincoln issued a few months after Antietam, further discouraged the British from intervening on the side of the Confederacy. The Emancipation Proclamation declared that all slaves in Confederate territory would be free, and it made the war a moral crusade for the abolition of slavery. The British public was strongly opposed to slavery, and they did not want their country to be associated with a regime that was based on it.
As a result of Antietam and the Emancipation Proclamation, the British government remained neutral throughout the Civil War. This was a major blow to the Confederacy, which had hoped for British support. The Union ultimately won the war, and the Confederacy was defeated.