Throughout June, Confederate General Robert E. Lee's Army of Northern Virginia was on the move. He had pulled his army from its position along the Rappahannock River around Fredericksburg, Virginia, and set it on the road to Pennsylvania. Lee and the Confederate leadership decided to try a second invasion of the North to take pressure off Virginia and to seize the initiative against the Army of the Potomac. The first invasion, in September 1862, failed when the Federals fought Lee's army to a standstill at the Battle of Antietam in Maryland.
Lee later divided his army and sent the regiments toward the Shenandoah Valley, using the Blue Ridge Mountains as a screen. After the Confederates took Winchester, Virginia, on June 14, they were situated on the Potomac River, seemingly in a position to move on Washington, D.C. Lincoln did not know it, but Lee had no intention of attacking Washington. All Lincoln knew was that the Rebel army was moving en masse and that Union troops could not be certain as to the Confederates' location.
On June 15, Lincoln put out an emergency call for 100,000 troops from the state militias of Pennsylvania, Maryland, Ohio, and West Virginia. Although the troops were not needed, and the call could not be fulfilled in such a short time, it was an indication of how little the Union authorities knew of Lee's movements and how vulnerable they thought the Federal capital was.