You’re missing the Chinese Civil War, which started in the 20s and didn’t conclude until after WW2.
"...and he did, because you did, because his parents, and your parents, because America, because England, because ancient Rome, because primordial ooze."
While you can model the world like this, one of the issues is often determining the "first mover", as it is hard to reasonable assert that the complexities of our world are primarily caused by primordial ooze. To continue the reduction, someone could come and say "Because a molten earth" after "Because primordial ooze" and there isn't necessarily grounds to refute that if the "Because primordial ooze" point was accepted.