Why was the War Between The States so particularly bloody and the casualty rates so epizootic in proportion?
Because both sides were American, and Americans don't quit.
Oh, the technology part is easy to explore, and the fact that everyone except a few guy like Forrest had learned from Napoleon's playbook.
Re: the standard "rifles behind cover firing on lines of guys in the open" argument, in his The Rifle Musket in Civil War Combat: Reality and Myth Hess argues that the new rifle-musket technology itself, because of the way it was actually deployed and used, had but little effect on the death toll....
"...if the gentlemen of Virginia shall send us a dozen of their sons, we would take great care in their education, instruct them in all we know, and make men of them." Canasatego 1744
