The USSR would've conquered all of Europe if it weren't for Germany - read _Icebreaker_, et. al. by Suvorov.
They might have tried.
Of course, without the Axis, Europe and the US would be firmly aligned against the USSR; the simultaneous existence of the Axis (which was more overtly expansionist) and the Soviet Union (whose ideology was more hostile to capitalist enterprise) split the capitalist West between those more concerned about the threat of Fascism and those more concerned about the threat of Communism.
edit: also, watch this: https://www.youtube.com/watch?v=ZOtinTlx7yo
At the end of the war, Soviets were in Berlin. If they were bent on continental domination, they could've fairly easily taken the rest of the exhausted Europe. Instead, luckily, the Allies managed to work out a peace agreement that held until the shockingly peaceful dissolution of the USSR, despite several close calls.
From Patton's journal, taken from The Patton Papers, 1940–1945, edited by Martin Blumenson:
> 18 May
> In my opinion, the American Army as it now exists could beat the Russians with the greatest of ease, because while the Russians have good infantry, they are lacking in artillery, air, tanks, and in the knowledge of the use of the combined arms’ whereas we excel in all three of these. If it should be necessary to fight the Russians, the sooner we do it the better.
Hmm... and what do you imagine the Americans would have been doing while this was going on, given that they still had a gigantic and completely undamaged industrial economy (the only one left in the world, at that stage), nuclear weapons, and truly massive amounts of troops and equipment that would have been available for redeployment from the Pacific after Japan's surrender?