The Russian Empire fell because the ruling Czarist aristocracy during the WWI lost the support of the urban middle class. The chaos created by the war resulted in a surge of peasant revolution. A disruption of state administration made possible the power grab by a small group of radical Socialists, the Bolsheviks, who were backed by the military in Petrograd (now St. Petersburg).
Which led to a tripartite Civil War between: (1) the old elite, (2) the Communists, supported by ethnic minorities and a large part of the military, (3) peasant gangs and armies. The support of peasants throughout 1919 secured the victory of Bolsheviks who established a kind of truce with them in 1922 in the form of a peasant-friendly New Economic Policy (NEP).
Stalin’s collectivization of 1928–1933, when private farmers were made de-facto state serfs, marked the ultimate defeat of the Russian peasant revolution and the final triumph of Communist revolutionaries.
The book “The Russian Revolution”, by Richard Pipes is probably the most succinct and accessible about the matter. Albeit it’s viewed by many in Russia and among leftist liberals in the West as biased against the revolutionaries, its factual base and the competence of the author are irrefutable.