After the fall of Pol Pot's regime, Cambodia came under Vietnamese military occupation,[7] and a pro-Hanoi, Soviet government known as the People’s Republic of Kampuchea was formed, led by the Kampuchean United Front for National Salvation.

After the fall of the Khmer Rouge and the conflict with Vietnam, Cambodia's economic situation was disastrous, with the plundering of the country's resources by Vietnamese troops only making matters worse.

In the summer, an armed group favourable to the former monarch, the Movement for the National Liberation of Kampuchea (MOULINAKA), was founded on the border with Thailand to fight against the Vietnamese occupier.

In April 1979, it had around ten thousand refugees transported by the Thai army to the mountainous region of Sok Sann, opposite the province of Chanthaburi, which he declared a "liberated zone" and from where he launched appeals to his compatriots.

[21] During the summer of 1979, the Khmer Rouge took advantage of the monsoon that hampered the movement of Vietnamese troops to reorganize themselves to launch offensives, renaming their armed forces to the National Army of Democratic Kampuchea.

[27] The United States gave the People's Republic of China a carte blanche on the Cambodian problem and continues to recognize Democratic Kampuchea as the government of Cambodia, mostly to mark its opposition to the USSR-supported Vietnamese occupation.

On the other hand, China and the United States only agreed to subsidize the Sihanoukist resistance if the prince formed an anti-Vietnamese coalition with the Khmer Rouge, which could provide him with troops.

On 4 September 1981, Sihanouk, Khieu Samphân and Son Sann published a joint statement announcing the formation of a coalition government to liberate Cambodia from "Vietnamese aggressors".

[31] Under the encouragement of China, which threatened to stop delivering weapons, the West, and ASEAN the three factions formed the Coalition Government of Democratic Kampuchea (GCKD) on June 21, 1982, in Kuala Lumpur.

However, he assigned himself the role of presidency of a "Higher Institute of National Defense", a position with vague responsibilities but which seemed to indicate that the former general secretary of the Communist Party of Kampuchea maintained leadership of the Khmer Rouge troops.

China, willing to put the USSR in difficult situations in the region, continued to fuel the Khmer Rouge rebellion without openly approving Pol Pot's "excesses" as it once did.

The new Soviet leader also expressed, in a speech delivered on July 24, 1986, the desire for rapprochement with the People's Republic of China, with which the Cambodian conflict remains the main dispute.

Vietnam, which was also experiencing economic difficulties, then realized that it could not count for long on the support of the USSR, whose help was financially essential to continue the war: it accelerated the withdrawal of its troops from Cambodia, which had already begun several years earlier.

[45] In 1987, France and Australia launched the project for an international conference responsible for drawing up a peace plan: negotiations were, however, destined to stumble for several years due to the role reserved for the Khmer Rouge.

[46] On December 2, 1987, in Fère-en-Tardenois, then on January 20–21, 1988 in Saint-Germain-en-Laye, Norodom Sihanouk and Cambodian Prime Minister Hun Sen met to reach an agreement on the opening of negotiations between all resistance factions and the Phnom Penh government.

[47] In July 1988, representatives of the KPNLF, the Khmer Rouge, FUNCINPEC, and the government of the People's Republic of Kampuchea met in Bogor, Indonesia, and proposed the formation of a national reconciliation council.

[24] Thailand, in the same period, changed its line of conduct to accelerate the Vietnamese withdrawal from Cambodia: Thai Prime Minister Chatichai Choonhavan initiated a rapprochement with Vietnam and the People's Republic of Kampuchea to favor commercial relations with these two countries.

The United States, in turn, wanted the establishment of an independent, but also anti-Vietnamese, Cambodian government, which would be formed by the forces of Son Sann and Sihanouk, possibly with the support of the Khmer Rouge.

The People's Republic of Kampuchea, whose legitimacy as an interlocutor has been recognized by all parties involved, proceeds at the end of April for a constitutional revision to woo the Sihanoukists: the regime abandons any reference to Marxism–Leninism and takes the official name of " State of Cambodia".

In November 1989, Australian Prime Minister Gareth Evans proposed placing Cambodia under UN trusteeship until elections, which eliminated the threat of monopolization of power by the Khmer Rouge.

In June 1990, Hun Sen suggested that the future coalition government, which would be called the Cambodian Supreme National Council (CNS), would have equal representatives from the State of Cambodia and the GCKD.

The Khmer Rouge agreed to this unfavorable agreement under joint pressure from China, which wanted to improve its international image and put an end to the quarrel with the USSR, and Thailand, in a hurry to normalize its relations with other states in the region.

Having not given up on regaining power, the Khmer Rouge didn't allow the United Nations peacekeeping Forces to enter the areas they control; in addition to continuing to harass the government army.

[56] Having lost the support of China, which distanced itself from them after realizing its electoral failure, as well as Thailand and Western countries, the Khmer Rouge can count on other financial resources, with the sale of mining rights for precious stones (rubies and sapphires).

[55] On 6 July 1994, the Cambodian assembly declared the Khmer Rouge "outlawed" and the two prime ministers asked the UN to establish a special court to try the leaders of Democratic Kampuchea.

Ieng Sary, who has lost influence over the years within the Khmer Rouge, is concerned about internal tensions within the movement: he responds to General Nhiek Bun Chhay's offers and, on August 8, 1996, announces his break with Pol Pot and their mobilization for government forces.

FUNCINPEC engages in secret negotiations with several opposition parties and several of its cadres contact the Khmer Rouge to forge a military alliance with them against Hun Sen. On June 1, Norodom Ranariddh meets Khieu Samphân on the border between Cambodia and Thailand.

A few days later, he publicly announced his agreement with the Khmer Rouge, specifying that he was planning the exile of Pol Pot, Son Sen, and Ta Mok, considered the most radical leaders of the movement.

Ta Mok then becomes terrified and decides, to avoid suffering the same fate as Son Sen, to take the lead: his men attack Pol Pot's troops, who are soon captured.

While the PPC removed FUNCINPEC from power, the Khmer Rouge settled their scores: on July 25, Pol Pot was publicly tried and sentenced to “life imprisonment” – in effect, house arrest – by his former subordinates.