These incursions would result in the Cambodian–Vietnamese War in which the newly unified Vietnam overthrew the Pol Pot regime and the Khmer Rouge, in turn ending the Cambodian genocide.

Chinese armed forces launched a punitive operation (Sino-Vietnamese War) in February 1979 and attacked Vietnam's northern provinces, determined to contain Soviet/Vietnamese influence and prevent territorial gains in the region.

[9][10] In order to acquire full control over Cambodia the People's Army of Vietnam needed to dislodge the remaining Khmer Rouge leaders and units, which had retreated to the remote areas along the Thai-Cambodian border.

[13] Disagreements over technical assistance for developing China's nuclear weapons and basic economic policies further alienated the Soviets and the Chinese as opposing forces of communist influence across the globe.

Permanently stationed North Vietnamese troops secured and maintained vital supply routes and strategic staging sites (Ho Chi Minh trail).

[15] From 1958 on, Northern and Southern Vietnamese combat troops also began to infiltrate the remote jungles of eastern Cambodia where they continued the Ho Chi Minh trail.

Armed border clashes between Cambodia and Vietnam soon flared up and escalated as Khmer Rouge forces advanced deep into Vietnamese territory and raided villages, killing hundreds of civilians.

Vietnam counterattacked and in December 1978, NVA troops invaded Cambodia, reaching Phnom Penh in January 1979 and arriving at the Thai border in spring 1979.

[20][5] However, as China, the U.S. and the majority of the international community opposed the Vietnamese campaign, the remaining Khmer Rouge managed to permanently settle in the Thai-Cambodian border region.

In a United Nations Security Council meeting, seven non-aligned members drafted a resolution for a ceasefire and Vietnamese withdrawal which failed due to opposition from the Soviet Union and Czechoslovakia.