The majority of this post will be coming from Zubok and Pleshakov's "Inside the Kremlin's Cold War". They submit that Stalin, who was a both a committed bolshevik and a student of Russian history, was motivated by what they call the "Revolutionary-Imperial" paradigm. The idea is that Stalin wanted the same old concerns of the older Russian imperial leaders (Territory for security, European respect/fear, etc.) but had to bend them to the prism of Marxist-Leninist ideology. So, for Stalin, he was really motivated by the desire for power and security for Russia's endless borders, as all Russian leaders had been, but had to reconcile that with his Communist/Marxist-Leninist ideology.