The Federal army reaches Centreville in northern Virginia, while Joseph E. Johnston’s Confederates slip out of the Shenandoah Valley undetected and head east.
The largest army ever assembled in North America went into motion at 2 p.m., starting the great campaign that many hoped would end the war.
President Lincoln holds a special cabinet meeting to decide on a plan for immediate offensive operations in northern Virginia.
Professor Thaddeus Lowe ascends in a balloon to demonstrate the usefulness of aerial military reconnaissance, and J.D. Mills demonstrates a forerunner to the modern machine gun.
The first land battle of the war takes place in northern Virginia, and Confederates blockade the Potomac waterway into Chesapeake Bay.
Federal troops pour into Washington and talk quickly turns from defense to offensive operations.