By early July 1861, there were over 40,000 men in and around Washington, D.C., and another 25,000 in the Shenandoah River Valley. Many of them were scheduled to depart soon, however; practically all of them had volunteered for three months only.

Lincoln and his commanders—East and West—faced a continuing problem throughout 1861: how to integrate militia units into the Regular Army. In some cases it just was not possible. Lincoln, therefore, believed it necessary to strike a first blow at the Confederacy before these men’s enlistments were up. He pressed General Winfield Scott, who pressed General Irvin McDowell (1818–1885). When McDowell complained to Lincoln that his men were “green” (or untried), the president replied that the Confederates were green as well and that the time had come to strike a blow.