The attack on the Soviet Union was inevitable. The politics of the NSDAP, the rhetoric about Lebensraum and so on, plus the fact that Stalin's Soviet Union posed, or would soon pose a serious threat to Germany. It is likely that, if Hitler hadn't attacked the Soviet Union in 1941, the Soviet Union would have attacked Germany in 1942 or later, if Stalin considered it to be to his advantage.
Some other alternate timelines to consider:
- Italia doesn't invade Greece. Germany does not have to save the Italian's butt there, and Operation Barbarossa starts earlier. Moscow falls before winter and the Russians are forced to retreat beyond the Urals. They are not beaten yet, but seriously weakened.
- Battle of Britain is won by Germany for some reason. (Focus on airfields and industry instead of civil population, even more ships sunk in the atlantic
, the evacuation of Dunkerque fails or, I'm getting slightly nationalist here,
Blücher is not sunk in the Oslo fjord, the king and government of Norway is captured, and Nortraship is never established.) Britain surrenders.