See, now that is a "what if" scenario that I can't see happening because with Adolph Hitler at the helm, there is no way there was not going to be a WW2. But to me, the most fascinating "what if," as far as WW2 is concerned, is what if England had lost the Battle of Britain. It was a close thing, and certainly could have happened. The world we know, today, would have been completely different.
The war in the West would have been over. There is no way it could have gone on without Great Britain. Hitler could have thrown the entire might of The Third Reich at the Soviets. Europe and the Middle East would have been his. All of the natural resources and all of the oil he needed. I have no doubt in my mind the USSR would have been defeated. Winter or no Winter. Von Paulus would not have had Hungarian and Romanian units protecting his flanks. He would have had German divisions there and they would not have crumbled. The 6th Army would not have been surrounded. Stalingrad would have fallen to the Nazis.
Canada would have been at war with Germany, but now, cut off from Europe, she would have been alone, hoping that the United States would join her. The U.S. would certainly have goten into it, eventually. Japan, seeing Germany's victory, would undoubtedly have attacked the U.S. in the Pacific. With things going well in Russia, Germany would have declared war on the United States and U-Boats would have joind the Japanese in making the seas around the North and South American continents a shipping graveyard.
Things would only get worse from there. I really think the Battle of Britain was THAT important.


"From our orbital vantage point, we observe an earth without borders, full of peace, beauty and magnificence, and we pray that humanity as a whole can imagine a borderless world as we see it, and strive to live as one in peace."
Astronaut William C. McCool RIP, January 29, 2003 - Space Shuttle Columbia