Before communism, Russia was a monarchy, an autocratic regime lead by a Tsar. This regime ended in the year of 1917 with the February Revolution of 1917
This Revolution was originated as a reaction to the Tsar policies, and because under his rule, the participation of Russia in the World War I left the country in bad conditions. It began as an spontaneous popular demonstration due to poor living conditions. Soon, the military, socialists and liberals joined the revolution. The goal was to overthrow the King and stablished a democratic regime.
However, the differences between the new leaders triggered inestability, which led to the October Revolution of 1917 which ended with the bolshevik victory. By the end of the October Revolution, Soviet Russia was stablished and the Russian Civil War iniciated in order to hold the power by the bolsheviks. The change can be considered as gradually since it took 2 revolutions and a civil war to maintain, but also it was not the result of a policy evolution or minor reforms, but violent imposition.