I would state the Soviet victory in the Russian Civil War as a really unlikely thing.
Only a tiny minority of the population was communist, the whites were supported by a host of great powers, and concurrent nationalist rebellions made things even more complex for the Soviets.
How the Soviets solved the situation had some semblance of Prussias exploits in the 7 years war.
The Soviets were much better at politics than their rivals and the support by the Great Powers was rather weak given that sending men to die in a foriegn land was quite unpopular after have just done that in WW1.
However early soviet losses in their civil war had the great benefit of realizing that they needed to move the capital from St Petersberg (aka Leningrad) to the old one of Moscow, if the capital was still Leningrad in WW2 the Soviets would have been in some serious trouble since they were such a centralized state and all railroads and communications were centered around the capital.