What event finally led to a successful revolution in russia? what group led this revolution and who was their leader?

The event that would lead to a successful Russian Revolution of 1917 would be World War I where Russia joins the war on the side of the Allied Powers. The revolution topples the power of the Tsars and replaced by a provisional government which later on will be toppled by the Communist led by Vladimir Lenin and the Bolsheviks who later will establish the Union Socialist of Soviet Russia (USSR).