<I don't think it's necessarily true that Nazi Germany would have won WWII if the United States had not entered that conflict.

Agreed, and Bowser documents the situation quite well.

Still, if America had sat out the conflict, maybe the Japanese WOULD have opened a second front on the Soviets.

One would have to know more about the history of WWII than I do to accurately predict the outcome of the war without the U.S. But there are only a few possible results.

There would probably have been a massive war between the U.S.S.R. and Germany, with all of Europe, much of north Africa, and most of Asia under the control of one or the other. If one or the other won an outright victory, they would take over whatever territory the other had absorbed. Whether the Eastern Hemisphere is under the boot of Stalin or Hitler probably makes little difference to those under the boot.

Maybe they would have struck an uneasy peace, and divided the nations between them. Not likely--such regimes thrive on conflict--but the result would have been the same. The boot on the neck.

These scenarios assume that America has some magic defense that allows neutrality. In real life, the Nazis were already developing methods of lofting bombs across the Atlantic. The V-2 was just the start. And let's not even think about what would have happened if they had developed nuclear weapons long before a "pacifistic" America.

The main point is regardless of who would have won a war between Nazism and Communism, most of humanity would have lost.