Thanks for the reply, so in the long run do you think the allies will win, even if the Second world war lasts one or two more years longer?
The odds are very strongly in favor of the western allies winning the war with a PoD close to the start of it. The combined technological, industrial, geographic, and leadership picture gave them a number of powerful advantages.
There are a lot of paths you can go down - if the five major power blocs (US, Entente, Axis, USSR, Japan) don't line up as they were at the end of 1941, a LOT is going to change.
Big questions to answer:
When does the US join the war? As long as FDR lives and the Entente don't do something massively stupid, the US is almost certain to wind up at war with Germany at some point.
Is it a three (or more) way war, with each power at war with all the others, or a two-and-a-half war, with the Entente (and later US) at war with both the Axis and the USSR, but the USSR and Germany at least neutral towards each other?
How does Japan fit in? WWII can't really go well for them, but they're a bit of a wild card. A more internationally minded government might plausibly come to power and seek alignment with
any of the other four blocs to fight one or more of the others; some of those alliances may be hard to swallow (especially Japan aligned with the USSR), but remember they sided with the Entente in WWI. Realpolitik can make for strange alliances. Who they side with (or against) and when will certainly have an impact on the entire shape of the war.
Is the atomic bomb developed roughly on OTLs schedule? While the practical effects of the 1st generation bombs weren't all that impressive from a purely military standpoint, their political and psychological effect was huge. Any PoD before August 2, 1939 might have as a butterfly preventing the "Einstein letter" from reaching FDR, and even PoDs after that could easily result in a slower (or faster) Manhattan Project for a variety of reasons. Just as one example: it is pretty clear today that the KGB had the Manhattan project thoroughly penetrated. If they were hostile to the US instead of semi-allied, might they sabotage it? One small bomb blowing up the right room of scientists and engineers might delay the project by years.