Long story short: World War II
is fought using modern tech (and in some cases, more than modern tech).
Part of the backstory was that the Anti War
and hippy/beat movement came out of World War One
instead of... you know... the fifties and sixties. World War One
in that timelime was controversial (it would be if it was fought today) and would be a backstory for some of the characters, and, of course, lead up to this to that timeline's World War II