The Antietam Campaign

(Wikipedia) The Maryland Campaign, or the Antietam Campaign (September 4–20, 1862) is widely considered one of the major turning points of the American Civil War. Confederate Gen. Robert E. Lee's first invasion of the North was repulsed by Maj. Gen. George B. McClellan and the Army of the Potomac, who moved to intercept Lee and his Army of Northern Virginia and eventually attacked it near Sharpsburg, Maryland. The resulting Battle of Antietam was the bloodiest single-day battle in American history.
Following his victory in the Northern Virginia Campaign, Lee moved north with 55,000 men through the Shenandoah Valley starting on September 4, 1862. Continued