Long convinced of their right to lead a confederation of communist Indochinese states, the authorities in Hanoi were startled and angered by the violent anti-Vietnamese policy of Democratic Kampuchea, manifested in both the incursions on the border and purges of Khmer cadre trained in Vietnam. Democratic Kampuchea in a 1978 Livre Noir accused Vietnam of trying to manipulate its politics and to assassinate its leaders, which, if so, had been unsuccessful. As the two former comrade communist governments fell out, the Vietnamese turned to building within Vietnam a rival Khmer communist movement. This was created out of communist cadre and others who had fled Cambodia in December 1977 - January 1978. This new Khmer communist organization was called the National United Front for the Salvation of Kampuchea (KNUFNS).

The Vietnamese, in the wake of their offensive of January 1979, installed their Cambodians as the People's Republic of Kampuchea. The ruling group, the People's Revolutionary Council, was headed by President Heng Samrin and Defense Minister Pen Sovan (later purged). The new regime at first was but a shadow, with the Vietnamese providing in the midst of the starvation what little government there was.

Gradually the new regime achieved substance as the few educated Khmer left were reemployed, as new people were trained, and as the Vietnamese turned over some authority. The regime was compromised by the popular perception of it as a creature of the Vietnamese, but it was sustained by popular relief at being rid of the Pol Pot regime. By 1983, the country was relatively secure except for the northeast and the far west and northwest. This depended, however, on the presence of a Vietnamese army of about 180,000 men, who conducted major campaigns, particularly during the dry seasons, against the Khmer Rouge and against the non-communist resistance forces, including Son Sann's Khmer People's National Liberation Armed Forces, Sihanouk's FUNINPEC and its military organization, the Armee Naionale Sihaoukienne. The PRK's own forces of about 30,000 were mainly employed then in static defense and as auxiliaries for the Vietnamese.

China and ASEAN pressed an international effort to deny recognition of the legitimacy of the new regime. As part of its effort to give an appearance of permanence, a new communist party called the People's Revolutionary Party of Kampuchea was established. Elections for a National Assembly were held in May 1981. A degree of normalcy returned, although the new government remained deeply dependent on Vietnam and desperately short of what it took to govern a country well.

As time passed, however, it gathered further the form and substance of real government, with some prosperity, peace, and corruption returning to Phnom Penh, although much less so in the countryside, particularly in the contested areas of the west.

Prime Minister Hun Sen, under the October 1992 Paris agreement, accepted a UN sponsored peace accord which reduced his government officially to just one of the four contending factions. The party was renamed the Cambodia People's Party. The official name of the country became simply "Cambodia". After the surprisingly successful free elections under UN auspices, the country again became the "Kingdom of Cambodia", although many of the military officers in new uniforms were those left over from the People's Republic and the former communists retained most of their power.