Although General Robert E. Lee had won Second Manassas, Pope's army was not destroyed. In fact, with reinforcements arriving and some forces relatively fresh from seeing little action at Manassas, Pope had some advantage over Lee's battle-weary troops.

However, to Lee's advantage, many of Pope's commanders were confused and disorganized. With Pope's lack of leadership, and Lee so close to Washington, Union leaders were caught trying to make up their minds as to their best course of action. After much vacillation, Pope finally decided to move toward Washington before Lee's Army of Northern Virginia could get between his army and the capital.

Early in the morning, General Lee crossed Bull Run with Major General J. E. B. Stuart and Robertson's Cavalry Brigade. A few miles further east on Warrenton Turnpike, they encountered units from the IX Corps at Cub Run. This let Lee know that Pope was on the defensive and would offer no fight except from the strong position on the Centreville ridge.

Lee considered his options... flanking south and east toward Fairfax Station and Annandale would go over rough country and poor roads with possible exposure to Major General Nathaniel Banks' II Corp (known to be guarding Pope's communication lines around Fairfax Station). North and east became the only logical choice. The roads were more developed, there would be fewer streams to cross, and the countryside was more open. Lee ordered Major General Thomas J. "Stonewall" Jackson  to circle the Union army on their right flank, by heading north to the broad, surfaced Little River Turnpike.