A major complaint detailed in the Declaration of Independence had to do with warfare being waged on civilian populations through native proxies, a process that was waged the other direction with nearly equal deadliness. French, English and Spanish governments all tried that technique in one direction or another at one time or another.
As far as medicine goes, yes, to be wounded in battle during that time was often simply a slower way of dying due to wound sepsis, communicable diseases, and complications of the crude surgery of the day that sometimes took years to kill. Best of luck coming up with any epidemiological figures for that. Something a little worrisome is the assumption that any civil war fought today will be fought under conditions of modern medicine. It strikes me that dust-off flights, transfusions, antibiotics, et al, may come into short supply if we are unfortunate enough to have to go at it again. It would certainly be very, very ugly.
I don't think many people realize how small our reserve medical capacity is. For us to have any significant such reserve, we'd have to have large buildings and many, many people waiting around for something bad to happen. Which we obviously don't.
At present additional capacity is added in disaster by bringing in out-of-area resources.
But what you do when all areas are affected?