OK, I'm playing with this idea for while.
Russian civil war somehow ends in the stalemate. The Soviets failed to defeat Whites in Siberia, and the Whites failed to recapture Moscow and Petrograd.
In 1920 Lenin and Kolchak signed a peace agreement and divided a former empire.
West of the Urals is the Soviet Union, and east of the Urals is restored Russian Empire. Central Asia is also divided, so Russian empire secured its food supplies.
The history of the Soviet Union is the same as in the OTL. Hitler comes to power, as in OTL, Stalin comes to power as in OTL.
During interwar period Soviets and Whites are living under bitter peace. Russian Empire is pretty similiar to fascist Italy, emperor (Cyril, I guess) is pretty much puppet of Kolchak's government. Would RE sign Anti-comitern pact? Would it align with Japan? Would US and UK help Soviets?
So nazis are coming, Poland is divided, and Barbarossa starts as in OTL.
What happens next?