Pure accident.
A Confederate officer had dropped a set of Lee's orders in the field, and they were discovered by Union troops.
These orders revealed that Lee's divisions were widely separated, giving McClellan a chance to destroy them piecemeal.
He did not move quite fast enough to achieve this. Also a Confederate spy in the Union camp was able to get word to Lee of what had happened, and he hastily concentrated his forces.
But the result was a Union victory - and a very historic one.
McClellan forced Lee to retreat at Antietam.
George McClellan (Union) and Robert E. Lee (Confederate).
Lincoln was disappointed that General George B. McClellan had allowed Confederate general Lee to escape after the Battle of Antietam. The result of Lincoln's disappointment was the replacement of McClellan by General Burnside.
His plans were found wrapped around some cigars and taken to McClellan.
The Battle of Antietam, an important battle of the Civiil War, was fought by the Army of the Potomac, part of the Union Army, under the command of General George McClellan, and Confederate forces under the command of General Robert E. Lee on September 17, 1862.
Antietam
McClellan forced Lee to retreat at Antietam.
McClellan for the Union. Lee for the Confederates.
Antietam
The commander of the Unions Army of the Potomac at Antietam was Major General George B. McClellan.
Robert E. Lee, AND George McClellan
General McClellan found General Lee's battle plan.
yes
The Battle of Antietam.
Confederate: Robert E. Lee ,,, Union: George B. McClellan
That he failed to pursue Lee after Antietam.
George McClellan (Union) and Robert E. Lee (Confederate).