By 1921, Russia had fallen to Communism and was remained the Union of Soviet Socials Republic (USSR)

In Communism, almost all decisions are made by the government.  In theory, there are no classes meaning no poor, and no wealthy.  However, there is virtually no choice in a Communist state.  Communism preaches "you get what you need, not what you want."   

Socialism is a delicate balance between the needs of the individual and the government.

 Socialist governments provide a great deal of services for the citizens but at a cost.  Socialist governments often have higher tax requirements but offer most social services for no cost under government program such as education and healthcare.  There is still choice in the market but less than capitalism 

Capitalism teaches that individuals should make decisions in the country.  Decisions on government and the market are made by consumers.

In Capitalism, the market makes the decisions based on supply and demand.  Government's role is limited so there is a wide range of choice.  In Capitalism, there are social classes but movement between those social classes is greater than Communism and Socialism.