On alternative histories
Incidentally, although there is no way to "prove" an alterative history, in a few cases it amounts to "proving" that dropping an elephant onto a raw egg will break it without actually performing the experiment.
I said that if the U.S. had stayed out of WWII that the outcome would have been Europe being either enslaved to the Soviets or to the Germans, but by all means, you are welcome to come up with a third scenario, if you can find one that's remotely plausible.