The commander of the Unions Army of the Potomac at Antietam was Major General George B. McClellan.
McClellan was a Union commander and he repelled general Lee's first Northern invasion.
During the seven day battles
He was too cautious and would not pursue Lee's army .
George B. McClellan & Robert E. Lee
Antietam Creek, near Sharpsburg, Maryland.
McClellan forced Lee to retreat at Antietam.
A set of Lee's orders, which had been dropped in the field by a careless Confederate officer. These orders revealed that Lee's divisions were widely separated, and that McClellan could destroy them, one by one. Unfortunately for McClellan, there was a Confederate spy in his camp, who was able to alert Lee of what had happened, and Lee was able to concentrate his troops. Still, McClellan's position was favourable, and if he'd moved fast enough, he could still have destroyed Lee's army. Instead, Lee was able to escape back to Virginia - for which McClellan was finally removed from command.
The commander of the Unions Army of the Potomac at Antietam was Major General George B. McClellan.
General McClellan found General Lee's battle plan.
The two Union armies under McClellan and Pope were in a position to combine within a few days, when they would have overwhelmed Lee's Army of Northern Virginia. Lee could only avert this by moving quickly enough to defeat Pope's army, before McClellan could reach the spot. Lee and Pope happened to clash at the old battlefield of Bull Run/Manassas. Hence '2nd Bull Run'.
McClellan for the Union. Lee for the Confederates.
McClellan was a Union commander and he repelled general Lee's first Northern invasion.
George McClellan (Union) and Robert E. Lee (Confederate).
In late October General McClellan finally began to move the Army of the Potomac but he hoped to disguise his operations. He did not try to beat Lee to Richmond. McClellan's objective was to threaten Lee's lines of communication and force Lee to remain in his location in order to do that.
During the Peninsula campaign, Union General George B. McClellan learned that Robert E. Lee had replaced the wounded Confederate General Joseph Johnston. In his memoirs, McClellan wrote that he was glad at the prospect of engaging Lee. McClellan wrote that Lee was too cautious and weak. And, that Lee lacked the moral fiber to use firmness in battlefield actions.
McClellan was very cautious, which was his biggest fault. And, Lee's record had taught the Federals that he was not to be trifled with, so everything had to be perfect for them to attack Lee. Lee serenely awaited an attack for a day after Antietem, but McClellan simply didn't have the guts to do it. He could have wrecked Lee, but didn't, as both armies were mauled severely by the battle.