WWI. I could see huge team battles doing trench warfare, dogfighting in planes...idk dodging mustard gas to shank the enemy in close quarters, using more "obsolete" guns (i.e. not the guns that came around in WWII like better machine guns and assault rifles and all that.) They could bring in the tanks that came around during the end of the war, you know, those hot, clunky metal contraptions, those would take tactics to take down especially with less effecient explosives and whatnot.
btw im not an expert on this war, so if i'm a little wrong in any assumptions, thanks for letting me know.
btw im not an expert on this war, so if i'm a little wrong in any assumptions, thanks for letting me know.