Short answers, pulled from the story.
Communism is a political and economic ideology whose goal is a society built on common ownership of the means of production, distribution, and exchange, with products allocated based on need. A communist society entails the absence of private property and social classes, and ultimately of money and the state. It is part of the broader socialist movement.
Karl Marx and Friedrich Engels offered a new definition of communism in The Communist Manifesto in 1848. The pamphlet popularized the term and proposed a particular type of communism rooted in class analysis.
The Soviet Union was dissolved on the 26th of December 1991, following declaration number 142-N of the Soviet of the Republics of the Supreme Soviet. That evening at 7:32, the Soviet flag was lowered from the Kremlin for the last time and replaced with the pre-revolutionary Russian flag.
States controlled by Communist parties under a single-party system include China, Cuba, Laos, North Korea, and Vietnam. Except for North Korea, these have allowed more economic competition while maintaining one-party rule.
Marxism-Leninism was developed by Joseph Stalin and rested on dialectical materialism, the leading role of the Communist party through democratic centralism, and a planned economy. Trotskyism, developed by Leon Trotsky, supported permanent revolution and world revolution rather than socialism in one country. Maoism, derived from Mao Zedong, held that peasants should be the bulwark of revolutionary energy led by the working class.
Communism's decline has been attributed to economic inefficiency and to authoritarianism and bureaucracy within Communist governments. With the dissolution of the Soviet Union in 1991, many governments abolished Communist rule, leaving only a few nominally Communist states.
Estimates of deaths under Mao's government range from 40 to 80 million through starvation, persecution, prison labour, and mass executions. The Great Leap Forward of 1957 to 1961 led to mass famine, and the years 1958 through 1961 were the only ones between 1953 and 1983 in which China's economy saw negative growth.