American Civil War: Union and Confederate Armies Move Toward Manassas #history #Union #Confederate July 21, 1861 — The First Battle of Bull Run, or Manassas, marked the first major clash of the American Civil War. Both sides expected a short, glorious fight. Instead, they met a brutal awakening on the rolling fields of Virginia. This animated battle map traces the battle hour by hour — from the early Union advance under Brig. Gen. Irvin McDowell to the Confederate counterattack led by Brig. Gen.