Gettysburg: Marching/running/riding into massed muskets filled with mini-balls, and cannon fire with grape, cannon balls and chain. Unbelievable courage at horrendous cost. I can’t imagine a more horrible battle. Men and horses lost footing, falling & floundering on the blood soaked ground. 51,112 in total died in battle and later from wounds (http://www.army.mil/Gettysburg).
624,511 of our best men died in the entire Civil War in addition to the near total devastation of the South. It took over a century to reach a semblance of recovery.