George B. McClellan

Recorded sideUnited States (Union)

Recorded resulttactical draw / strategic victory

Tactically inconclusive; Lee withdrew back to Virginia, ending his first invasion of the North

Lee, badly outnumbered, used interior lines and the terrain to shift defenders to each threatened sector; McClellan's piecemeal, uncoordinated attacks and failure to commit reserves let the Confederates survive, though the strategic result forced Lee's retreat.

What followed

The bloodiest single day in U.S. history. Though tactically a draw, halting Lee's invasion gave Lincoln the victory he needed to issue the preliminary Emancipation Proclamation, reframing the war around ending slavery and discouraging European recognition of the Confederacy.

Recorded sideUnited States (Union)

Recorded resultvictory

Union victory; Confederates forced from the mountain gaps but bought time to concentrate at Sharpsburg

Acting on Lee's captured Special Order 191, McClellan pushed through the South Mountain gaps; superior Union numbers eventually forced the outnumbered Confederate defenders off the heights, though the stubborn defense delayed the Union advance long enough for Lee to regroup at Antietam.

What followed

First major clash of the Maryland Campaign, three days before Antietam. Union Major General Jesse L. Reno was killed here; the city of Reno, Nevada, is named in his honor. The battle forced Lee to abandon his campaign plan and consolidate at Sharpsburg.