Following the failure of General George McClellan’s campaign against Richmond, General Robert E. Lee reorganized, replenished, and restructured his army by creating two corps under Generals James Longstreet and Thomas Jackson.  At the same time, Union General John Pope proposed that McClellan’s forces on the Peninsula should join his army in Northern Virginia.  He could then advance upon Richmond from the north and overwhelm Lee through sheer force of numbers.  President Abraham Lincoln approved and ordered McClellan to comply.

Never one to concede the initiative, and outraged by the conduct of Pope’s soldiers in Northern Virginia, Lee sent Jackson north to engage the scattered elements of Pope’s army before it could unite.  “Stonewall” Jackson acted aggressively and moved against his old Valley opponent, General Nathaniel Banks, near Culpeper.  The two forces met in the Battle of Cedar Mountain on August 9, where Jackson emerged victorious.

Spurred by Jackson’s victory, and convinced that McClellan was not a threat, Lee shifted Longstreet north of Richmond and launched a sweeping offensive against Pope’s forces.  Jackson conducted a rapid march to the west around Pope’s right flank while Longstreet followed behind.  Jackson’s march was so rapid that he destroyed Pope’s supply depot at Manassas Junction before he could react. 

With Federal forces converging on his corps, Jackson took up defensive positions on the old Manassas battlefield.  He ambushed elements of Pope’s army near Groveton on August 28 initiating the Battle of Second Manassas, where, joined by Lee and Longstreet after the latter forced the passage of Thoroughfare Gap, they routed Pope’s army.  Lee pursued Pope aggressively, and Jackson caught up with the Federal rear guard during the Battle of Chantilly. Pope managed to reach Washington, D.C.’s defenses, but his defeat opened the road for an invasion of the North.