The Soviets were not bent on world conquest, but on securing a ring of buffer states around them as security for their country. Witness Stalin's betrayal of the communists in Greece as horse trading for influence elsewhere. Stalin's socialism in one country policy set against exporting revolution was in fact a huge point of contention with other factions of the Bolsheviks.
While the Soviets did harbour imperial ambitions against neighbouring states (Poland, Finland), this:
> had Hitler not attacked first, Stalin would probably just attack Germany within a short period of time
is blatantly false, and insultingly so given the millions of Soviet citizens who paid a bloody price for Stalin's total lack of readiness at the German border or mobilization against the Nazis.