As we all know, the USSR was the leading power of the Comintern (also including the German People's Republic, People's Republic of Spain, and China) against the Allied Powers (UK, France, USA, Japan, and Italy) during the Second Great War (also famously known as "The Red Peril"). But I had an idea which is quite strange, and I know that most would probably call this ASB, but how can you get the USSR to join the Allies in an alternate WW2, assuming it wasn't a war against the Comintern? What possible threat could arise that would make the USSR join the side of the Allies, and what about the other side? What would it be comprised of? Could the other side perhaps be fascist?