The battle was over by 5:30 p.m. Losses for the day were heavy on both sides. The Union had 12,401 casualties with 2,108 dead. Confederate casualties were 10,318 with 1,546 dead. This represented 25% of the Federal force and 31% of the Confederate. More Americans died on September 17, 1862, than on any other day in the nation's military history, including World War II's D-Day and the terrorist assaults of September 11, 2001. On the morning of September 18, Lee's army prepared to defend against a Federal assault that never came. After an improvised truce for both sides to recover and exchange their wounded, Lee's forces began withdrawing across the Potomac that evening to return to Virginia.President Lincoln was disappointed in McClellan's performance. He believed that McClellan's cautious and poorly coordinated actions in the field had forced the battle to a draw rather than a crippling Confederate defeat.
Historian Stephen Sears agrees." In making his battle against great odds to
save the Republic, General McClellan had committed barely 50,000 infantry and
artillerymen to the contest. A third of his army did not fire a shot. Even at
that, his men repeatedly drove the Army of Northern Virginia to the brink of
disaster, feats of valor entirely lost on a commander thinking of little beyond
staving off his own defeat." Stephen W. Sears, Landscape Turned Red