B. Christopher Frueh and Jeffrey Allen Smith ask this about mental trauma and the Civil War:
One would assume that the physical price paid by the men who fought in the war would have a rough equivalent in the mental price, that the experience of that terrible war would have left countless survivors with horrible psychological scars. But that may not actually be the case: according to official Union war records, adverse psychological reactions to combat across a variety of categories never matched, or even approached, the shocking physical losses from the war…
Nevertheless, what should be made of the relatively low-recorded instances of psychological casualties in the Civil War? Was it a result of flawed data collection or analysis? Did Victorian or religious social pressures result in under reporting or unwillingness to recognize these invisible wounds?
Ultimately, they conclude:
While considering diagnoses of modern psychiatric conditions extrapolated from records kept 150 years ago during the Civil War is problematic at several levels, perhaps the larger take away message is a heartening one of human resiliency. The data seem to demonstrate that exposure to combat alone does not weaken the human psychological condition.
I think there’s something else going on. The Civil War, by and large, was set piece war in a culturally familiar environment. Unlike many modern conflicts, where death potentially lurks around every corner and soldiers can’t tell friend from foe, typically Civil War battles were more clearly defined, and the combat portion was relatively short and defined; the battle of Gettysburg, for instance, was less than 72 hours long. That doesn’t mean there weren’t ‘meat-grinder’ battles or that war wasn’t terrifying. But it wasn’t constant, and there were many familiar touchstones of home. There was some respite from battle, whereas in many conflicts, the threat of death is all pervasive. If you’re not paranoid, there’s a good chance you will be.
That has to be a factor.