The battle of Antietam was the single bloodiest day of the American Civil War and is considered one of the major turning points of the war. It was the first two attempts by Robert E. Lee to go on the offensive and take the war onto northern soil and into the Union. The battle was significance because it forced the confederate army to retreat back across the Potomac River. President Lincoln saw the significance of the battle and in turn issued the famous Emancipation Proclamation in 1862.