Under Sihanouk, the People's Social Community Party (Sang Kam) was the most important political group. In the 1955, 1958, 1962, and 1966 elections, with a platform of nonalignment, economic aid, and development, it captured all seats in the National Assembly. Exiled in Beijing following his overthrow by Lon Nol in March 1970, Sihanouk allied himself with Cambodia's leftist insurgents under a group called the National United Front of Kampuchea (Front National Uni de Kampuchea—FNUK). Under the Khmer Republic government headed by Lon Nol, five political groups came to the fore. The Socio-Democratic Party (SDP), Lon Nol's own group, was quickly established as the most powerful political organization. Centrist opposition groups included the Republican Party and the Democratic Party. In the presidential elections held in June 1972, Lon Nol, the SDP's candidate, won by a relatively narrow margin of 55%.
With the victory of their forces in April 1975, leaders of the pro-communist FNUK became the dominant political power in Kampuchea. The leading element in FNUK was the Khmer Communist Party (KCP), founded in 1951 and now dominated by radicals Pol Pot (previously known as Saloth Sar) and Khieu Samphan. Khieu Samphan was named prime minister of the new regime, while Pol Pot remained party head. During the next few years the Pol Pot faction systematically purged all suspected pro-Vietnamese members of the party organization. In late 1978, opposition elements, headed by Heng Samrin, formed the Kampuchean National United Front for National Salvation (KNUFNS) in an effort to overthrow the Pol Pot regime. Following a Vietnamese invasion in December, Heng Samrin became the head of the pro-Vietnamese PRK government installed in January 1979. In 1981, the KNUFNS was renamed the Kampuchean United Front for National Construction and Defense, the primary mass organization in the PRK. Popularly known as the Khmer Rouge, the movement allied during the 1980s with two non-Communist factions, the Sihanoukists and Son Sann's KPNLF.
The Coalition Government of Democratic Kampuchea (CGDK), the tripartite, anti-Vietnamese resistance group formed in June 1982, changed is name to the National Government of Cambodia (NGC) in 1990. Autonomous coalition members were the Sihanoukist FUNCINPEC, the KPNLF, and the Khmer Rouge. Prince Sihanouk's main political organization, formed in 1981, was known as the National United Front for an Independent, Neutral, Peaceful, and Cooperative Cambodia, or its French acronym, FUNCINPEC; he resigned as its head in 1989. In 1992 the Front was registered as a political party for the 1993 elections and Prince Norodom Ranariddh was elected president.
In 1992 the Khmer People's National Liberation Front (KPNLF), headed by Son Sann, formed the Buddhist Liberal Democratic Party (BLDP), also headed by Son Sann. The military wing of the KPNLF was the KPNLAF, the Khmer People's National Liberation Army formed under Son Sann in 1979. Although it boycotted the elections and attempted to undermine the peace process, the Khmer Rouge had also formed a party to contest the elections, the Cambodian National Unity Party, headed by Kieu Samphan and Son Sen.
The Kampuchean People's Revolutionary Party (KPRP), the Communist Party originally installed by Vietnam in 1979 as the People's Republic of Kampuchea (PRK), was also known as the Heng Samrin Government in the late 1980s. In 1991 the KPRP dropped the word "Revolutionary" from the party name, becoming the Khmer People's Party or Cambodian People's Party (CPP). Hun Sen remained Chairman of the Council of Ministers of the government of the State of Cambodia a position he had held since 1985. At an extraordinary party congress, 17–18 October 1991, Chea Sim was elected party president, replacing Heng Samrin, and Hun Sen was elected party vice president; these events signaled a shift from hardline communist ideology to a reformist position prior to the UN-supervised elections. Chea Sim remained president of the National Assembly.
In the coalition government following the 1993 election, Hun Sen was made Second Premier, and FUNCINPEC's Ranariddh became First Premier. Hun Sen was able to push Ranariddh out of that position with 1997's brutal coup d'etat, and the CPP won enough seats in the 1998 election to establish Hun Sen as sole prime minister.
Perennial opposition leader and anti-corruption crusader Sam Rainsy transformed his unrecognized Khmer Nation Party into the eponymous Sam Rainsy Party, which won significant Assembly seats in the 1998 election. Sam Rainsy has repeatedly stooped to race-baiting directed against Cambodia's Vietnamese population during his political career. At the same time, he is an eloquent spokesman for increased democratization and openness in Cambodia, and a persistent anti-authoritarian thorn in Hun Sen's side. In early 2000, Sam Rainsy brought the question of royal succession into the open, which seems to provoke Hun Sen's fear that his arch rival, Prince Ranariddh of FUNCINPEC, could possibly follow his aged, ailing father, Prince Sihanouk, to the throne of Cambodia's constitutional monarchy.
In May 2002, Prince Ranariddh's half-brother formed a new party, the Prince Norodom Chakrapong Khmer Soul party, to contest the national elections to be held in July 2003. Prince Ranariddh warned that the new party would split the royalist vote and ensure continued dominance by Hun Sen. Prince Norodom Chakrapong offered to form an alliance with the Sam Rainsy Party.