Following the Union Army’s embarrassing defeat at the First Battle of Bull Run, Joseph Hooker was appointed brigadier general and ordered to defend Washington, D.C., from further Confederate incursions. Wasting no time, Hooker quickly established a large encampment just outside the city, where he first commanded a brigade, then a division, as part of the effort to organize and train the new Army of the Potomac, under Maj. Gen. George B. McClellan.