Would Hitler have won World War II if he had left Russia alone?

[Algernon Moncrieff]

18. Hitler's goal was never to "leave Russia alone"

But let's play "what if":

You have several factors:

What does Russia do while Hitler is doing other things? Stand still? Invade?
What does the US do?
What does Japan do?

Assuming that '39 went the way it went, and the invasion of France succeeds, Hitler's next logical step would be to conquer England. His best shot of doing that was in '40, when the Luftwaffe had superiority over the RAF pre Battle-of-Britain. So let's say they proceed with Operation Sea Lion: they would have to win a quick, decisive victory over Great Britain (like in under a month). If they get bogged down in a battle for England, a) Russia probably invades Germany (via Poland) pro-actively and b) America probably enters the war in Europe far earlier.

If you are playing alternate history, here are more interesting questions:

a) Suppose Hitler backs away from anti-semitism? Many of the scientists who give America the A-bomb fled Germany.
b) In December 1941, suppose Japan choses to take Vladivostok and invade Kamchatka and Siberia instead of bombing Pearl Harbor. A beleaguered Russia now has to fight on two fronts, and the US may not enter the war until '42 -- if at all.