After a very indecisive but bloody Peninsular Campaign and one year after the first Bull Run Lincoln and his advisers felt that it was time to try a new general in place of McClellan, so they agreed on John Pope, who had been fairly successful in the west. Second the Cabinet decided that the following major forces in the North should come together: the armies of the Valley were to unite under John Pope; then Burnside was ordered north from Fortress Monroe to Falmouth; finally McClellan was directed to bring his great army to Alexandria and unite with Pope.
There was one major flaw in the Unions complex maneuvers. They had forgotten that Lee's Army of Virginia was located between all of them. Beginning an excellent general Lee seized the moment to attack the individual armies before they converged to beat an almost unbeatable force. After a sharp fight at Cedar Mountain near Culpeper Court House Jackson swung around to attack a supply depots and Pope's headquarters at Manassas Junction on August 26. At the time Pope was trying gather his army at Rapidian. Quickly Pope turned to try and corner Jackson and he thought he had him but Jackson marched west to Groveton and invited Pope's attack. With Jackson's soldiers used to the long marches they had no trouble holding off Pope's following army near Groveton. As the fighting was occurring near Groveton, Longstreet was hurrying up the valley between the Blue Ridge and the Bull Run Mountains. On the twenty-ninth he turned up east, forced Thoroughfare Gap-Which pope had left practically undefended-and the next day struck Pope's left flank, defeated it, and sent the whole army reeling toward Bull Run.
The battle ended in a cloud of confusion and doubts about just how loyal the Union army was to each other. Porter's corps had stood idle the whole afternoon of the twenty-ninth; Banks's 6,500 men had taken no part in the fight; McClellan, at near-by Alexandria, had failed to get any part of his large army to Pope in time to do any good. Porter was later made the scapegoat for all this tragedy of errors, but the real failure was Pope's and McClellan's.
To Lee this battle was great victory, for it drove the Union out of Virginia and Lee than could drive the war up to the North. The Union needed a victory soon.