Causes of civil war
there were many causes of the Russian Civil War, the Tsar was far too arrogant and was seen as a horrible decision maker (he was). The Russian Empire had began modernizing, but was far too primitive for it's own survival. Russia had however won the Russo-Japanese war (even though they suffered massive casualties) and was only really stable at all because of this. WW1 way over-stressed the nation and given the Tsar's horrible decisions (not mobilizing military etc.) it was just a matter of time before something happened.
The Russian Civil War
On 12th June 1916 the Tsar abdicated after an attempted (but failed) assassination attempt. Russia pretty well collapsed and on 14th February 1917 The Bolsheviks and the United Republic of Russia Committee (OTL Whites) rebelled. A small Fascist rising in Downtown Moscow failed horribly as the Bolsheviks killed all the Fascists. St. Petersburg is home of the Republic of Russia Committee. However, St. Petersburg is soon renamed "Rusinia" by the Committee. The civil war was quickly over, the Committee was defeated in a matter of weeks as they only had 15,000 men. The Bolsheviks had 150,000 men already and simply annihilated the Committee. In the end, Communism prevailed. Rusinia is renamed to Leningrad (kinda like in OTL).