Stalin was just as responsible for starting the war as Hitler.
And the Russian Revolution did just as much to spawn the hellish events of the 20th Century — and ended up taking millions more victims than Nazism.
Stalin was counting on a long war of attribution in the West between Britain, France and Germany, as in WWI. What he didn't count on was France falling without much of a fight, which kept the British and German armies largely intact, and Germany strong enough to try to invade the Soviet Union. Stalin was hoping for a few more years to build the Red Army back up, after the 1938 Purges, that's why he went out of his way to not provoke the Germans, despite the intelligence telling him an attack was imminent.