The horror of the mechanized aggression of WWII and WWI frequently pales in comparison to many battles fought mono-e-mono in bygone centuries.
We still talk about Guadacanal and Iwo Jima in hushed tones. Our casualties were around 20,000/island after the dust cleared. Horrible to be sure.
There have been a great many battles with casualties exceeding 80,000 men in a single day.
There are exceptions like The Battle of the Bulge, Stalingrad, and others.
What were the casualites at Gettysburg? That was about the worst day of Civil War.