Communism is an ideology that seeks to establish a classless, stateless social organization based on common ownership of the means of production. It is usually considered a branch of the broader socialist movement that draws on the various political and intellectual movements that trace their origins back to the work of Karl Marx. However, communism had a rich history of theory and practice for hundreds of years before Marx's attempt to think communism in the context of industrialization. Communism as a political goal is generally a conjectured form of future social organization, although Marxists have described early forms of human social organization as "primitive communism". Self-identified communists hold a variety of views, including Marxism Leninism, Trotskyism, council communism, Luxemburgism, anarchist communism, Christian communism, and various currents of left communism, which are generally the more widespread varieties. However, various offshoots of the Soviet (what critics call the "Stalinist", and supporters call Marxist-Leninist) and Maoist interpretations of Marxism comprise a particular branch of communism that has the distinction of having been the primary driving force for communism in world politics during most of the 20th century. The competing branch of Trotskyism has not had such a distinction.
Karl Marx held that society could not be transformed from the capitalist mode of production to the advanced communist mode of production all at once, but required a transitional period which Marx described as the revolutionary dictatorship of the proletariat, the first stage of communism. The communist society Marx envisioned emerging from capitalism has never been implemented, and it remains theoretical; Marx, in fact, commented very little on what communist society would actually look like. However, the term "Communism", especially when it is capitalized, is often used to refer to the political and economic regimes under communist parties that claimed to embody the dictatorship of the proletariat.
In the late 19th century, Marxist theories motivated socialist parties across Europe, although their policies later developed along the lines of "reforming" capitalism, rather than overthrowing it. One exception was the Russian Social Democratic Labour Party. One branch of this party, commonly known as the Bolsheviks and headed by Vladimir Lenin, succeeded in taking control of the country after the toppling of the Provisional Government in the Russian Revolution of 1917. In 1918, this party changed its name to the Communist Party, thus establishing the contemporary distinction between communism and other trends of socialism.
After the success of the October Revolution in Russia, many socialist parties in other countries became communist parties, signaling varying degrees of allegiance to the new Communist Party of the Soviet Union. After World War II, communists consolidated power in Eastern Europe, and in 1949, the Communist Party of China (CPC) led by Mao Zedong established the People's Republic of China, which would later follow its own ideological path of communist development. Among the other countries in the Third World that adopted a pro-communist government at some point were Cuba, North Korea, North Vietnam, Laos, Angola, and Mozambique. By the early 1980s almost one-third of the world's population lived in Communist states.
Since the early 1970s, the term Eurocommunism was used to refer to the policies of reformist communist parties in western Europe, break with the tradition of uncritical and unconditional support of the Soviet Union. Such parties were politically active and electorally significant in Italy (PCI), France (PCF), and Spain (PCE).
There is a history of anti-communism in the United States, which manifested itself in the Sedition Act of 1918, the subsequent Palmer Raids, and the later period of McCarthyism.
With the decline of the communist governments in Eastern Europe from the late 1980s and the breakup of the Soviet Union on December 9, 1991, communism's influence has decreased dramatically in Europe. However, around a quarter of the world's population still lives in communist states, mostly in the People's Republic of China. There are also communist movements in Latin America and South Asia that have significant popular support.

Main article: History of communism