Just after the Cold Harbor fight outside Richmond in early June, Robert E. Lee felt a threat to his rear. This was the small army of David Hunter, come east from the West Virginia mountains and down to Lynchburg east of the Shenandoah Valley. Hunter was a threat to Lee's supplies as well as a possible reinforcement for Grant, who was banging on the doors of Petersburg and Richmond. Lee detached General Jubal Early and his corps of 8,000 soldiers to push Hunter out of Lynchburg and relieve the pressure from this sector. If he could do that then he could return to Lee or march north in a raid toward Washington.

Early joined with the Confederate force that had recently defeated Sigel, and they pursued Hunter until the Union general had taken his army back into the West Virginia hinterland, leaving the entire Shenandoah Valley free of significant Union forces. Early and Lee were positioned to use the Shenandoah Valley as a kind of shotgun pointed toward Washington, D.C.

Even if the Confederates could not capture the capital they would likely frighten Lincoln into demanding a substantial force be recalled to man the Washington defenses. This would leave Grant weakened at a time when Northern sentiment was turning sour.

Early continued north, bypassing a strong Union garrison at Harpers Ferry, and crossed the Potomac near the old Antietam battlefield. Grant detached troops from his lines near Petersburg to reinforce Washington. Some of these men defended a line along the Monocacy River outside Frederick, Maryland. Early's Southerners defeated them and pressed on toward Washington, but the fight at the Monocacy River had delayed Early just enough to allow more of Grant's men to fill the Washington forts and trenches north of the city. When Early reached Washington on July 11 and 12, he determined he could not breach the defenses and so withdrew toward the Shenandoah Valley whence he came.