 A year and a half later, the single bloodiest day of combat in American military history occurred during the first major Confederate invasion of the North in the Maryland Campaign, just north above the Potomac River near Sharpsburg in Washington County, at the Battle of Antietam on September 17, 1862.Preceded by the pivotal skirmishes at three mountain passes of Crampton, Fox and Turner's Gaps to the east in the Battle of South Mountain, Antietam (also known in the South as the Battle of Sharpsburg), though tactically a draw, was strategically enough of a Union victory in the second year of the war to give 16th President Abraham Lincoln the opportunity to issue in September 1862, the Emancipation Proclamation, taking effect January 1, 1863, which declared slaves in the rebelling states of the Confederacy (but not those in the areas already occupied by the Union Army or in border slave states like Maryland, Delaware, Kentucky, and Missouri) to be "henceforth and forever free".Later, in July 1864, the Battle of Monocacy near Frederick, Maryland in the third and last major Southern invasion, was also fought on Maryland soil.