Why was the battle of Antietam a crucial victory for the union.

The Battle of Antietam was a crucial victory for the Union Army, because was the first major battle in the American Civil War to take place on their soil. It was also the bloodiest battle of the war and was a victory for the Union Army, because the Confederate Army retreated first and gave President Abraham Lincoln the confidence to do the Emancipation Proclamation, subtracting the power of France and the United Kingdom to be in support of the Confederate side.