Communism as a theory of government and social reform may be said, in a limited sense, to have begun with the ancient Greek idea of the Golden Age, a concept of a world of communal bliss and harmony without the institution of private property. Plato, in his Republic, outlined a society with communal holding of property; his concept of a hierarchical social system including slavery has by some been called "aristocratic communism."

The Neoplatonists revived the idea of common property, which was also strong in some religious groups such as the Jewish Essenes and certain early Christian communities. These opponents of private property held that property holding was evil and irreligious and that God had created the world for the use of all humanity. The first of these ideas was particularly strong among Manichaean and Gnostic heretics, such as the Cathari, but these concepts were also found in some orthodox Christian groups (e.g., the Franciscans).

The manorial system of the Middle Ages included common cultivation of the fields and communal use of the village commons, which might be vigorously defended against the lord. It was partly to uphold these common rights, threatened by early agrarian capitalism, that the participants in the Peasants' Revolt (1381) in England and the insurgents of the Peasants' War in 16th-century Germany advocated common ownership of land and of the means of production.

In the 16th and 17th cent. such intellectual works as Sir Thomas More's Utopia proposed forms of communal property ownership in reaction to what the authors felt was the selfishness and depredation of growing economic individualism. In addition, some religious groups of the early modern period advocated forms of communism, just as had certain of the early Christians. The Anabaptists under Thomas Münzer were the real upholders of communism in the Peasants' War, and they were savagely punished for their beliefs. This same mixture of religious enthusiasm and economic reform was shown in 17th-century England by the tiny sect of the Diggers, who actually sought to put their theories into practice on common land.

Capitalism, reinforced by the Industrial Revolution, which began in the 18th cent., brought about the conditions that gave rise to modern communism. Wages, hours, and factory conditions for the new industrial class were appalling, and protest grew. Although the French Revolution ended without satisfying radical demands for economic egalitarianism, the voice of François Babeuf was strongly raised against economic inequality and the power of private property. For his class consciousness and his will to revolution he has been considered the first modern communist. Although he was guillotined, his movement (Babouvism) lived on, and the organization of his secret revolutionary society on the "cell" system was to be developed later as a means of militant revolution.

In the early 19th cent. ardent opponents of industrial society created a wide variety of protest theories. Already what is generally known as utopian communism had been well launched by the comte de Saint-Simon. In this era a number of advocates gathered followers, founded small cults, and attempted to launch communistic settlements, particularly in the United States. Most notable among such men were Robert Owen, Étienne Cabet, and Charles Fourier. Pierre Joseph Proudhon, although he did not adopt the principle of common ownership, exercised great influence by his attacks on the evils of private property.

A host of critics and idealistic revolutionists arose in Germany, but more important was the survival or revival of Babouvism in secret French and Italian revolutionary societies, intent on overthrowing the established governments and on setting up a new, propertyless society. It was among them that the terms communism and socialism were first used. They were used vaguely and more or less interchangeably, although there was a tendency to use the term socialist to denote those who merely stressed a strong state as the owner of all means of production, and the term communist for those who stressed the abolition of all private property (except immediate personal goods). Among the chief leaders of such revolutionary groups were the Frenchmen Louis Blanc and (far more radical) Louis Auguste Blanqui, both of whom played important roles in the February Revolution of 1848.

The year 1848 was also marked by the appearance of The Communist Manifesto of Karl Marx and Friedrich Engels, the primary exposition of the socioeconomic doctrine that came to be known as Marxism. It postulated the inevitability of a communist society, which would result when economic forces (the determinants of history) caused the class war; in this struggle the exploited industrial proletariat would overthrow the capitalists and establish the new classless order of social ownership. Marxian theories and programs soon came to dominate left-wing thought. Although the German group (founded in 1847) for which The Communist Manifesto was written was called the Communist League, the Marxist movement went forward under the name of socialism; its 19th-century history is treated in the article under that heading and under Socialist parties, in European history.

The modern form of Communism (written with a capital C) began to develop with the split (1903) within the Russian Social Democratic Labor party into factions of Bolshevism and Menshevism. The more radical wing, the Bolsheviks, were led by Lenin and advocated immediate and violent revolution to bring about the downfall of capitalism and the establishment of an international socialist state. The triumph of the Bolsheviks in the Russian Revolution of 1917 gave them the leadership in socialist action. They constituted the Communist party in 1918 (see Communist party, in the USSR).

Meanwhile World War I had shaken the socialist movement as a whole by splitting those who cooperated with the governments in waging the war from those who maintained a stand for revolution against all capitalist governments. Chief among the stalwart revolutionists were the Communist party in Russia and the Spartacus party (later the Communist party) in Germany. The establishment of a working socialist state in Russia tended to give that country leadership, and Leninism grew stronger. Communist revolts immediately after the war failed in Germany, and the briefly successful Communist state under Béla Kun in Hungary was also repressed with great bloodshed.

The revolutionary socialists now broke completely with the moderate majority of the movement, withdrew from the Second International, and formed (1919) the Third International, or Comintern, in 1919. Henceforth, the term Communism was applied to the ideology of the parties founded under the aegis of the Comintern. Their program called for the uniting of all the workers of the world for the coming world revolution, which would be followed by the establishment of a dictatorship of the proletariat and state socialism. Ultimately there would develop a harmonious classless society, and the state would wither away.

The Communist parties were organized on a hierarchical basis, with active cells of members as the broad base; they were made up only of the elite—those approved by the higher members of the party as being reliable, active, and subject completely to party rule. Communist parties were formed in countries throughout the world and were particularly active in trying to win control of labor unions and in fomenting labor unrest.

Despite the existence of the Comintern, however, the Communist party in the USSR adopted, under Joseph Stalin, the theory of "socialism in one country," which asserted the possibility of building a true Communist system in one country alone. This departure from Marxist internationalism was challenged by Leon Trotsky, whose theory of "permanent revolution" stressed the necessity of world revolution. After Trotsky was expelled (1929) from the Soviet Union, he founded a Fourth, or Trotskyist, International to rival the Comintern.

Stalin's program of building the Soviet Union as the model and base of Communism in the world had the effect of tying Communist and Soviet policy even more closely together, an effect intensified by the "monolithic unity" produced by the party purges of the 1930s. It became clearly evident in that decade that in practice Communism, contrary to the hopes of theorists and intellectuals, had created in the USSR a giant totalitarian state that dominated every aspect of life and denied the ideal of individual liberty.

Except for the Mongolian People's Republic (see Mongolia, republic), no other Communist state was created before World War II. The Chinese Communist party was founded in 1921 and began a long struggle for power with the Kuomintang. However, it received little aid from the USSR, and it was not to achieve its goal until 1949.

In the late 1920s and early 30s the Communist parties followed a policy of total hostility to the socialists, and in Germany this was one factor that facilitated the rise of the Nazis. In 1935, however, the Comintern dictated a change in policy, and the Communists began to work with other leftist and liberal parties for liberal legislation and government, as in the Popular Front government in France.

In World War II the USSR became an ally of the Western capitalist nations after Germany attacked it in 1941. As part of its cooperation with the Allies, the USSR brought about (1943) the dissolution of the Comintern. Hopes for continued cooperation, intrinsic in the formation of the United Nations, were dashed, however, by a widening rift between the Soviet bloc and the Western democracies, especially the United States, after the war (see cold war).

Communism had been vastly strengthened by the winning of many new nations into the zone of Soviet influence and strength in Eastern Europe. Governments strictly modeled on the Soviet Communist plan were installed in the "satellite" states—Albania, Poland, Czechoslovakia, Hungary, Bulgaria, Romania, and East Germany. A Communist government was also created under Marshal Tito in Yugoslavia, but Tito's independent policies led to the expulsion of Yugoslavia from the Cominform, which had replaced the Comintern, and Titoism was labeled deviationist.

By 1950 the Chinese Communists held all of China except Taiwan, thus controlling the most populous nation in the world. A Communist administration was also installed in North Korea, and fighting between the People's Republic of Korea (Communist) and the southern Republic of Korea exploded in the Korean War (1950–53), fought between Communist and United Nations troops. Other areas where rising Communist strength provoked dissension and in some cases actual fighting include Malaya, Laos, many nations of the Middle East and Africa, and, especially, Vietnam, where the United States intervened to aid the South Vietnamese regime against Communist guerrillas and North Vietnam (see Vietnam War). In many of these poor countries, Communists attempted, with varying degrees of success, to unite with nationalist and socialist forces against Western imperialism.

After the death of Stalin in 1953 some relaxation of Soviet Communist strictures seemed to occur, and at the 20th party congress (1956) Premier Nikita Khruschchev denounced the methods of Stalin and called for a return to the principles of Lenin, thus presaging some change in Communist methods, although none in fundamental ideology. A resurgence of nationalist feeling within the Soviet bloc—as was vividly demonstrated by the bloodily suppressed Hungarian uprising of 1956—ultimately had to be acknowledged by the USSR. However, while the USSR began to allow some limited freedom of action to the countries of Eastern Europe, the invasion of Czechoslovakia in 1968 demonstrated its determination to prevent serious challenges to its domination.

Ideological differences between China and the USSR became increasingly apparent in the 1960s and 70s, with China portraying itself as a leader of the underdeveloped world against the two superpowers, the United States and the Soviet Union. Nonetheless, both the USSR and China sought better relations with the United States in the 1970s.