A little more on my theory above, but regarding Hitler's Germany.
Germany came very close to succeeding but eventually fell short due to military shortages. That's not the case for America if it indeed attempts world control without any significant competition. However, like an omen from above, assuming such a thing could exist, nuclear arms appeared on the world scene.
That deterrent has forever taken away the opportunity for another Hitler. Not Russia, China, the US, or any other major power can help itself to it all. It must now become a popularity contest amongst the world's superpowers.
Question: Are there other factors that can grant any of the big three more than their share?