This the name given to the left in Cambodian politics since the 1950s. However the name has come to be identified with a particular group since the 1970s - the Communist Party of Kampuchea (CPK), known during the 1980s and 90s as the "Party of Democratic Kampuchea."
Until the mid-1990s the leadership of the CPK was largely unchanged since the 1960s. The Standing Committee of the Central Committee ("Party Center") comprised Saloth Sar (known as Pol Pot), Nuon Chea, Chhit Choeun (known as Ta Mok), Khieu Samphan,Ke Pauk, Ieng Sary, Son Sen, Yun Yat, and Ieng Thirith.
The Khmer Rouge army (the National Army of Democratic Kampuchea), aided by North Vietnam, began a revolution in response in 1970, quickly gaining control over most of the country. In April 1975 they finally overthrew Lon Nol, to establish Democratic Kampuchea.
In an effort to create a classless utopian society the new government carried out a radical program (Year Zero) of emptying the urban areas, closing schools and factories, abolishing banking and currency, outlawing all religions, ending all private propery, and herding the population into collective farms. Intellectuals were targeted for murder. Depending on the source a reported 15% to 40% of the population died between 1975 and 1979 (1 to 3 million people).
The Khmer Rouge were also planning to regain land lost centuries ago to Vietnam. In 1978, after several years of border conflict, Vietnamese troops invaded in December, deposing the Khmer Rouge government within two weeks, by January 7, 1979. The Khmer Rouge, however, continued to control an area near the Thai border. In 1985 Khieu Samphan officially succeeded Pol Pot as head of the Khmer Rouge.
All Cambodian political factions signed a treaty in 1991 calling for elections and disarmament. But in 1992 the Khmer Rouge resumed fighting and the following year they rejected the results of the elections. There was a mass defection in 1996 when around half the remaining soldiers (about 4,000) left. Factional fighting in 1997 led to Pol Pot's trial and imprisonment by the Khmer Rouge. Pol Pot died in April 1998, and Khieu Samphan surrendered in December 1998. By 1999 most members had surrendered, or been captured.