The KR were strongly supported by the Chinese leading up to, during, and after their reign in 1975-79. It was the Chinese who insisted on the KR accepting Sihanouk as the figurehead of their revolution in 1970 after Lon Nol's coup in 1970. sihanouk's call to arms to join the Khmer Rouge was a major factor in the explosive growth of the KR after 1970. The North Vietnamese communists also provided support and advisory services to the KR up through around '77 by 1978 KR raids across the Vietnamese border had made it clear the KR had developed a strongly anti-Vietnam stance which lead to the invasion of Cambodia by Vietnam in 1978 along with rearmed former KR troops mainly from the Eastern Zone who had escaped the purges of '77 (eastern zone units and KR were suspected of having "Cambodian bodies with Vietnamese minds").

The Chinese invaded Vietnam briefly in 1980 in retaliation for the Vietnamese overthrow of the KR and installation of a puppet government in Phnom Penh. This also led to the rather awkward (now) situation of the KR continuing to be recognized by international law as the legitimate government of Cambodia since they were domestically originated and retaining the UN seat for Cambodia, while the Vietnam installed government was considered illegitimate by international law since it was installed due to invasion.