Disokong oleh:
China
 Amerika Syarikat
 United KingdomKonflik selepasnya:
 Thailand (Pertikaian sempadan)Jumlah: 50,000+ mati[2][4]Perang Kemboja-Vietnam merupakan satu konflik bersenjata yang berlaku di antara Republik Sosialis Vietnam dan Demokratik Kampuchea. Pada 25 Disember 1978, Vietnam telah melancarkan satu serangan mendadak ke atas Kemboja, dengan pantas berjaya mengalahkan rejim Khmer Rouge dan mengusir saki-baki tentera ke dalam Thailand. Vietnam melakukan serbuan ini bagi membalas provokasi Kemboja, apabila rejim Pol Pot bertindak secara ganas ke atas Vietnam, melakukan pembersihan etnik besar-besaran ke atas orang Vietnam yang tinggal di Kemboja, dan melancarkan satu siri serangan melepasi sempadan yang menyebabkan kematian ramai penduduk Vietnam.[6]Semasa Perang Vietnam, komunis Vietnam dan Khmer Rouge telah membentuk satu persekutuan untuk menentang rejim yang disokong oleh Amerika Syarikat di dalam negara mereka. Di sebalik kerjasama erat dengan Vietnam, kepimpinan Khmer Rouge gusar akan pihak komunis Vietnam cuba membentuk sebuah persekutuan Indochina dengan Vietnam sebagai pihak yang dominan di wilayah ini. Dalam satu usaha cubaan awal untuk mengagalkan usaha Vietnam, kepimpinan Khmer Rouge mula membersihkan anggota yang dilatih oleh Vietnam selepas rejim Lon Nol dijatuhkan pada tahun 1975. Then, in May 1975, the newly formed Democratic Kampuchea, dominated by the Khmer Rouge, began waging a war against Vietnam, which was marked by an attack on the Vietnamese island of Phu Quoc. In spite of the fighting that had occurred between the two countries, the leaders of reunified Vietnam and Kampuchea made several public diplomatic exchanges throughout 1976 to highlight the supposedly strong relations between them. However, behind the scenes, Kampuchean leaders continued to fear what they perceived as Vietnamese expansionism. As such, on 30 April 1977, they launched another major military attack on Vietnam. Shocked by the Kampuchean assault, Vietnam launched a retaliatory strike at the end of 1977 in an attempt to force the Kampuchean Government to negotiate. In January 1978, the Vietnamese military withdrew because their political objectives had not been achieved.Small-scale fighting continued between the two countries throughout 1978, as China tried to mediate peace talks between the two sides. However, neither country could reach an acceptable compromise at the negotiation table. By the end of 1978, Vietnamese leaders decided to remove the Khmer Rouge-dominated regime of Democratic Kampuchea, perceiving it as being pro-Chinese and too hostile towards Vietnam. On 25 December 1978, 150,000 Vietnamese troops invaded Democratic Kampuchea and overran the Kampuchean Revolutionary Army in just two weeks. On 8 January 1979, a pro-Vietnamese People's Republic of Kampuchea (PRK) was established in Phnom Penh, marking the beginning of a ten-year Vietnamese occupation. During that period, the Khmer Rouge's Democratic Kampuchea continued to be recognised by the United Nations as the legitimate government of Kampuchea, as several armed resistance groups were formed to fight the Vietnamese occupation. Behind the scenes, Prime Minister Hun Sen of the PRK regime approached factions of the Coalition Government of Democratic Kampuchea (CGDK) to begin peace talks. Under heavy diplomatic and economic pressure from the international community, the Vietnamese Government implemented a series of economic and foreign policy reforms, which led to their withdrawal from Kampuchea in September 1989.At the Third Jakarta Informal Meeting in 1990, under the Australian-sponsored Cambodian Peace Plan, representatives of the CGDK and the PRK agreed to a power-sharing arrangement by forming a unity government known as the Supreme National Council (SNC). The SNC's role was to represent Cambodian sovereignty on the international stage, while the United Nations Transitional Authority in Cambodia (UNTAC) was tasked with supervising the country's domestic policies until a Cambodian government was elected by the people through a peaceful, democratic process. Cambodia's pathway to peace proved to be difficult, as Khmer Rouge leaders decided not to participate in the general elections, but instead they chose to disrupt the electoral process by launching military attacks on UN peacekeepers and killing ethnic Vietnamese migrants. In May 1993, Sihanouk's FUNCINPEC movement defeated the Cambodian People's Party (CPP), formerly the Kampuchean People's Revolutionary Party (KPRP), to win the general elections. However, the CPP leadership refused to accept defeat and they announced that the eastern provinces of Cambodia, where most of the CPP's votes were drawn from, would secede from Cambodia. To avoid such an outcome, Norodom Ranariddh, the leader of FUNCINPEC agreed to form a coalition government with the CPP. Shortly afterwards, the constitutional monarchy was restored and the Khmer Rouge was outlawed by the newly formed Cambodian Government.