A way to Define Communism is to refer to it as a socioeconomic structure that promotes the establishment of a classless, stateless society 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 theorists of the Industrial Revolution and the French Revolution. Opponents say that communism is an ideology, whereas promoters say that it is the only political system without ideology, because it is the consequence of historical materialism and the revolution of the proletariat. Although many forms of communism, such as Leninism, Trotskyism and Luxemburgism, are based on Marxism and Karl Marx is sometimes known as the "father of Communism", non-Marxist versions of communism (such as Christian communism and anarchist communism) also exist.

Communism as a political goal is a 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. However, the offshoots of the Marxist-Leninist interpretations of Marxism are the most well-known of these and have been a driving force in international relations during most of the 20th century. Communists believe that the working class, also called the proletariat, would have to start a revolution in order to change from a competitive capitalist society to a co-operative communist society. 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. This government would represent the proletariat and suppress the Bourgeoisie's resistance to the revolution. The communist society Marx envisioned emerging from this intermediate phase 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 Bolshevik faction of the Russian Social Democratic Labour Party 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. Communists themselves repudiate the usage of the term "communist state", as a communist society by their definition is a state-less society. The terms used by the communist movement to describe these states are either socialist states or 'people's democracies'. 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.

Karl Marx saw primitive communism as the original, hunter-gatherer state of humankind from which it arose. For Marx, only after humanity was capable of producing surplus, did private property develop. At one time or another, various small communist communities existed, generally under the inspiration of Scripture. In the medieval Christian church, for example, some monastic communities and religious orders shared their land and other property. These groups often believed that concern with private property was a distraction from religious service to God and neighbor. Criticism of the idea of private property continued into the Age of Enlightenment of the 18th century. Later, following the upheaval of the French Revolution, communism emerged as a political doctrine. François Noël Babeuf, in particular, espoused the goals of common ownership of land and total economic and political equality among citizens. Narious social reformers in the early 19th century founded communities based on common ownership. But unlike many previous communist communities, they replaced the religious emphasis with a rational and philanthropic basis. In its modern form, communism grew out of the socialist movement of 19th century Europe. As the Industrial Revolution advanced, socialist critics blamed capitalism for the misery of the proletariat a new class of urban factory workers who labored under often-hazardous conditions. Foremost among these critics were the German philosopher Karl Marx and his associate Friedrich Engels. In 1848 Marx and Engels offered a new definition of communism and popularized the term in their famous pamphlet The Communist Manifesto. Engels, who lived in Manchester, observed the organization of the Chartist movement, while Marx departed from his university comrades to meet the proletariat in France and Germany.

Like other socialists, Marx and Engels sought an end to capitalism and the systems which they perceived to be responsible for the exploitation of workers. But whereas earlier socialists often favored longer-term social reform, Marx and Engels believed that popular revolution was all but inevitable, and the only path to socialism. According to the Marxist argument for communism, the main characteristic of human life in class society is alienation; and communism is desirable because it entails the full realization of human freedom. Marxism holds that a process of class conflict and revolutionary struggle will result in victory for the proletariat and the establishment of a communist society in which private ownership is abolished over time and the means of production and subsistence belong to the community. Marx himself wrote little about life under communism, giving only the most general indication as to what constituted a communist society. It is clear that it entails abundance in which there is little limit to the projects that humans may undertake. In the popular slogan that was adopted by the communist movement, communism was a world in which each gave according to their abilities, and received according to their needs. The German Ideology (1845) was one of Marx's few writings to elaborate on the communist future: In the late 19th century the terms "socialism" and "communism" were often used interchangeably.

Some of Marx's contemporaries espoused similar ideas, but differed in their views of how to reach to a classless society. Following the split between those associated with Marx and Mikhail Bakunin at the First International, the anarchists formed the International Workers Association. Anarchists argued that capitalism and the state were inseparable and that one could not be abolished without the other. Anarchist-communists such as Peter Kropotkin theorized an immediate transition to one society with no classes. Anarcho-syndicalism became one of the dominant forms of anarchist organization, arguing that labor unions, as opposed to Communist parties, are the organizations that can change society. Consequently, many anarchists have been in opposition to Marxist communism to this day.

Vladimir Lenin following his return to PetrogradIn the late 19th century Russian Marxism developed a distinct character. The first major figure of Russian Marxism was Georgi Plekhanov. Underlying the work of Plekhanov was the assumption that Russia, less urbanized and industrialized than Western Europe, had many years to go before society would be ready for proletarian revolution could occur, and a transitional period of a bourgeois democratic regime would be required to replace Tsarism with a socialist and later communist society. In Russia, the 1917 October Revolution was the first time any party with an avowedly Marxist orientation, in this case the Bolshevik Party, seized state power. The assumption of state power by the Bolsheviks generated a great deal of practical and theoretical debate within the Marxist movement. Marx predicted that socialism and communism would be built upon foundations laid by the most advanced capitalist development. Russia, however, was one of the poorest countries in Europe with an enormous, largely illiterate peasantry and a minority of industrial workers. Marx had explicitly stated that Russia might be able to skip the stage of bourgeois capitalism. Other socialists also believed that a Russian revolution could be the precursor of workers' revolutions in the West. The moderate Mensheviks opposed Lenin's Bolshevik plan for socialist revolution before capitalism was more fully developed. The Bolsheviks' successful rise to power was based upon the slogans "peace, bread, and land" and "All power to the Soviets", slogans which tapped the massive public desire for an end to Russian involvement in the First World War, the peasants' demand for land reform, and popular support for the Soviets. The usage of the terms "communism" and "socialism" shifted after 1917, when the Bolsheviks changed their name to the Communist Party and installed a single party regime devoted to the implementation of socialist policies under Leninism. The Second International had dissolved in 1916 over national divisions, as the separate national parties that composed it did not maintain a unified front against the war, instead generally supporting their respective nation's role. Lenin thus created the Third International (Comintern) in 1919 and sent the Twenty-one Conditions, which included democratic centralism, to all European socialist parties willing to adhere. In France, for example, the majority of the SFIO socialist party split in 1921 to form the SFIC (French Section of the Communist International). Henceforth, the term "Communism" was applied to the objective of the parties founded under the umbrella of the Comintern. Their program called for the uniting of workers of the world for revolution, which would be followed by the establishment of a dictatorship of the proletariat as well as the development of a socialist economy. Ultimately, if their program held, there would develop a harmonious classless society, with the withering away of the state. During the Russian Civil War (1918-1922), the Bolsheviks nationalized all productive property and imposed a policy of war communism, which put factories and railroads under strict government control, collected and rationed food, and introduced some bourgeois management of industry. After three years of war and the 1921 Kronstadt rebellion, Lenin declared the New Economic Policy (NEP) in 1921, which was to give a "limited place for a limited time to capitalism." The NEP lasted until 1928, when Joseph Stalin achieved party leadership, and the introduction of the first Five Year Plan spelled the end of it. Following the Russian Civil War, the Bolsheviks formed in 1922 the Union of Soviet Socialist Republics (USSR), or Soviet Union, from the former Russian Empire. Following Lenin's democratic centralism, the Communist parties were organized on a hierarchical basis, with active cells of members as the broad base; they were made up only of elite cadres approved by higher members of the party as being reliable and completely subject to party discipline. The Soviet Union and other countries ruled by Communist parties are often described as Communist states with state socialist economic bases. This usage indicates that they proclaim that they have realized part of the socialist program by abolishing the private control of the means of production and establishing state control over the economy; however, they do not declare themselves truly communist, as they have not established communal ownership of property.

Marxist-Leninism is a version of socialism, with some important modifications, adopted by the Soviet Union under Stalin. It shaped the Soviet Union and influenced Communist Parties worldwide. It was heralded as a possibility of building communism via a massive program of industrialization and collectivization. The rapid development of industry, and above all the victory of the Soviet Union in the Second World War, maintained that vision throughout the world, even around a decade following Stalin's death, when the party adopted a program in which it promised the establishment of communism within thirty years. Under Stalin, the Communist Party of the Soviet Union adopted the theory of "socialism in one country" and claimed that, due to the "aggravation of class struggle under socialism", it was possible, even necessary, to build socialism alone in one country, the USSR.

Maoism is the Marxist Leninist trend associated with Mao Zedong. After the death of Stalin in 1953, the Soviet Union's new leader, Nikita Khrushchev called for a return to the principles of Lenin, thus presaging some change in Communist methods. However, Khrushchev's reforms heightened ideological differences between the People's Republic of China and the Soviet Union, which became increasingly apparent in the 1960s. As the Sino-Soviet Split in the international Communist movement turned toward open hostility, China portrayed itself as a leader of the underdeveloped world against the two superpowers, the United States and the Soviet Union. Parties and groups that supported the Communist Party of China (CPC) in their criticism against the new Soviet leadership proclaimed themselves as 'anti-revisionist' and denounced the CPSU and the parties aligned with it as revisionist "capitalist-roaders."

Trotsky and his supporters organized into the Left Opposition, and their platform became known as Trotskyism. Stalin eventually succeeded in gaining control of the Soviet regime, and their attempts to remove Stalin from power resulted in Trotsky's exile from the Soviet Union in 1929. During Trotsky's exile, world communism fractured into two distinct branches: Marxism-Leninism and Trotskyism. Trotsky later founded the Fourth International, a Trotskyist rival to the Comintern, in 1938. Trotskyist ideas have continually found a modest echo among political movements in some countries in Latin America and Asia, especially in Argentina, Brazil, Bolivia and Sri Lanka. Many Trotskyist organizations are also active in more stable, developed countries in North America and Western Europe. Today, Trotskyists are organized in various international organizations and tendencies. However, as a whole, Trotsky's theories and attitudes were never accepted in worldwide mainstream Communist circles after Trotsky's expulsion, either within or outside of the Soviet bloc.

By virtue of the Soviet Union's victory in the Second World War in 1945, the Soviet Army had occupied nations in both Eastern Europe and East Asia; as a result, communism as a movement spread to many new countries. This expansion of communism both in Europe and Asia gave rise to a few different branches of its own, such as Maoism. Communism had been vastly strengthened by the winning of many new nations into the sphere of Soviet influence and strength in Eastern Europe. Governments modeled on Soviet Communism took power with Soviet assistance in Bulgaria, Czechoslovakia, East Germany, Poland, Hungary and Romania. By 1950 the Chinese Communists held all of Mainland China, thus controlling the most populous nation in the world.

In 1985, Mikhail Gorbachev became leader of the Soviet Union and relaxed central control, in accordance with reform policies of glasnost (openness) and perestroika (restructuring). The Soviet Union did not intervene as Poland, East Germany, Czechoslovakia, Bulgaria, Romania, and Hungary all abandoned Communist rule by 1990. In 1991, the Soviet Union itself dissolved. By the beginning of the 21st century, states controlled by Communist parties under a single-party system include the People's Republic of China, Cuba, Laos, North Korea, and Vietnam. Communist parties, or their descendant parties, remain politically important in many countries.

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