The Battle of Antietam, September 17, 1862, was the bloodiest day of fighting in the Civil War. The battle was significant for that reason and two others: Great Britain had been contemplating recognition of the Confederacy, but Lee's having to withdraw shorted that effort. Second, Lincoln used the "victory" to announce his preliminary Emancipation Proclamation, which altered the objectives of the war for the Union.
General
George B. McClellan had Robert E. Lee right where he wanted him a few
days before the great battle but let him slip away by delay and over-caution.
On the day of the battle Lee was hard pressed to defend his position against
the numerically superior Yankees, but again McClellan failed to press
the attack and let the Confederates off with a tactical draw. Lee escaped
back to Virginia, battered but prepared to fight on, as he did with ferocity
at Fredericksburg and Chancellorsville. McClellan might have ended the
war at Antietam in 1862, but with the slavery issue yet unresolved, peace
might well have been hard to keep.
Dunker Church after the battle in 1863.
Dunker Church as it appears today.