The Russian Civil War was fought between 1917–1923* and won by the Red Army led by the Bolsheviks. The many reasons for their victory were:
The anti-communist White Movement, which opposed the Bolsheviks, was a loose alliance and was not particularly cohesive. The Mensheviks and Socialist Revolutionaries opposed the Bolsheviks' power, the aristocracy wanted to restore the old order, landowners and factory workers had their property seized, and Orthodox Christians disagreed with the Bolsheviks' atheist viewpoints. The Constitutional Democratic Party wanted to keep fighting Germany. Even with a lot of foreign assistance, many still couldn't cooperate because they dreaded living in a communist society. It was simple for the Red Army to battle these little organizations one at a time.
Leon Trotsky was chosen by Lenin to lead the Red Army. Although some people objected to it, he appointed former royal army officers as his own, knowing that he required experienced commanders. He had the responsibility of building an army from scratch. Few people wanted to oppose Trotsky because he was a brilliant tactician.
Communism was the guiding philosophy of the Red Army, and those who supported it believed that fighting for it was the correct thing to do. Trotsky and many others envisioned a global communist revolution. Other than opposing the Bolsheviks, the Whites had no real beliefs.
Lenin created War Communism, in which the government nationalized all businesses and dictated what they should produce, in order to gain victory. They also forced peasants, both male and female, to labor in particular professions and let troops to confiscate food and other supplies from them. As a result of the Russian Revolution's lost liberties, many were hostile to the Bolsheviks. This even sparked rebellions like the sailors' uprising at Kronstadt. Leon stomped on them.
Additionally, the Bolsheviks maintained order during the Red Terror. The Communist Secret Police, Cheka, carried out the Red Terror campaign, which involved mass murdering anybody who resisted the Bolsheviks. There are between 10,000 and 1.5 million people.
All the significant regions of Russia were under the Red Army's authority. They held control of the railroads and the industrial districts of Moscow and Petrograd (Saint Petersburg). The other European nations were occupied with World War One and were unable to assist because of their own defeat.
