The “catalyst” for war between Russia and Germany was Hitler’s desire to convert most of the western USSR into “lebensraum” for greater Germany. The Slavic population of those areas was to be either killed outright, driven out to the East, or wiped out through gradual attrition using mandatory birth control, abortion, etc.
Stalin signed the Non-Aggression Pact, knowing the end result would be war between Germany France and Britain.
He counted on them all bleeding each other dry, allowing the Red Army to swoop in and take over the continent.
Just one problem, France fell without much of a fight, and Britain was neutralized, allowing Hitler to focus everything on attacking the Soviet Union.