My theory is that modern "combat PTSD" didn't happen widely until barrel rifling enabled artillery and snipers to hit targets from incredible distances. Before

My theory is that modern "combat PTSD" didn't happen widely until barrel rifling enabled artillery and snipers to hit targets from incredible distances. Before barrel rifling, if you weren't actively fighting, you weren't at too much risk of dying from an unseen enemy attack. You could let your guard down and take a rest when you needed to. But if artillery and snipers are on the board, death can come anywhere, any time. Soldiers are in "fight or flight" mode basically all of the time and they never get a break until their deployment is over. But by that point it's hard to turn off, so you end up with a bunch of traumatized soldiers poorly adapted to living in a peacetime society. From what we know about trauma, the more time you spend in "fight or flight" the greater your chances of developing PTSD. This is why guerilla tactics are so effective against a standing army: if you make sure the enemy never feels safe, they will eventually become so traumatized that they leave. People certainly got PTSD -- I'd be surprised if most women of certain eras weren't traumatized given the ever-present threat of rape -- but it was probably limited to the victims of war rather than the combatants.