Nothing. The fact that it took pretty much the entire world uniting to defeat them speaks loud and clear that this was the way. I write "was" because the world of the 1920s was vastly different from the world of the 2020s.

From the economic miracle to the military awesomeness, including the wholesomeness and sound morality of that culture, it was perfection. And THAT is why the demonic forces that already controlled the world back then absolutely NEEDED to defeat nazism. And to try to ensure it would never rise up again, go on to brainwash the masses into believing the most absurd of horrors on the part of the regime and its citizens.