Idk if I’d discount the brutality of Vietnam, between the cluster bombs and zippo raids and land mines and Agent Orange defoliant.
That war was about as brutal as it was possible to get, shy of nuclear strikes.
I think the WWs were, perhaps, more brief because of their scale. Very hard to maintain two fronts across central Europe for any length of time.
Vietnam was different for sure, but it just isn’t the same situation as a world war where multiple modernized military forces are going at it with the most cutting edge technology and tactics available. I think another reason world wars don’t last as long is because they are wars that are much harder to extract profit out of too. You have to sink an insane amount of resources into it at the cost of pretty much all other economic activity.
