 The Single Bloodiest Day in American History It s September 17, 1862 and President Abraham Lincoln needs a victory in order to issue the Emancipation Proclamation and end slavery in the South. But Robert E. Lee has other plans - invade the North. When Lee s strategy falls into the hands of the Union Army, the result is the single bloodiest day in American history at the Battle of Antietam in Sharpsburg, Maryland.