 And on 1 July 1863, during the Civil War, Union and Confederate forces collided at Gettysburg, Pennsylvania. The battle lasted three days and ended with a Confederate retreat. General Lee planned a northern invasion. His army, about 80,000, began moving on June 3. The Union army of 100,000 began moving shortly thereafter, staying between Lee and Washington, D.C. On June 28, George Meade assumed the Union command.