Lee begins moving his army northwest from Fredericksburg into the Shenandoah Valley, where the Blue Ridge Mountains screen their northward movements.

Joseph Hooker, still in command of the Army of the Potomac, sends cavalry forces to find Lee.

The clash at Brandy Station on June 9 is the largest predominantly cavalry battle of the war but ends inconclusively.

The Battle of Aldie in the Gettysburg Campaign ends inconclusively on June 17.

Tensions have grown between Hooker and his cavalry commander Brigadier General Alfred Pleasonton because of the latter's inability to penetrate Major General J.E.B. Stuart's cavalry screen and gain access to the Shenandoah Valley to locate the Army of Northern Virginia, which has been on the move since the Battle of Chancellorsville in early May.

Pleasonton had decided on June 17 to push through Stuart's screen.

To accomplish his goal, he had ordered Brigadier General David McMurtrie Gregg's division from Manassas Junction westward down the Little River Turnpike to Aldie.

Aldie is tactically important in that near the village the Little River Turnpike intersects both the Ashby's Gap Turnpike and Snicker's Gap Turnpike, which respectively lead through Ashby's Gap and Snickers Gap of the Blue Ridge Mountain into the valley.

Munford does not consider Aldie as a defeat as his withdrawal coincides with an order from Stuart to retire, as more Federal cavalry had been sighted at Middleburg.

Union casualties are three hundred and five dead and wounded, with the Confederates losing between one hundred and ten and one hundred and nineteen.

Aldie is the first in what will be a series of small battles along the Ashby's Gap Turnpike in which Stuart's forces successfully delay Pleasonton's thrust across the Loudoun Valley, depriving him of the opportunity to locate Lee's army.

Hooker had started his entire army in pursuit; over the past few weeks, Hooker has argued with both Lincoln and Halleck over the role of the garrison at Harpers Ferry.

On June 28, President Lincoln loses patience with him and relieves him of command, replacing him with V Corps commander, Major General George G. Meade.

After reviewing the positions of the army's corps with Hooker, Meade orders the army to advance into southern Pennsylvania in a wide front, with the intention of protecting Washington and Baltimore and finding Lee's army.

He also draws up plans to defend a line behind Pipe Creek in northern Maryland in case he cannot find suitable ground in Pennsylvania to fight a battle to his advantage.

Lee is surprised to find that the Federal army is moving so quickly.

As they cross the Potomac and enter Frederick, Maryland, the Confederates are spread out over a considerable distance in Pennsylvania, with Richard Ewell across the Susquehanna River from Harrisburg and James Longstreet and A. P. Hill behind the mountains in Chambersburg.

Lee's cavalry, under Jeb Stuart, is engaged in a wide-ranging raid around the eastern flank of the Union army and is uncharacteristically out of touch with headquarters, leaving Lee blind as to his enemy's position and intentions.

Lee realizes that, just as in the Maryland Campaign, he has to concentrate his army before it can be defeated in detail.

He orders all units to move to the general vicinity of Gettysburg, Pennsylvania.