Vietnamese invasion of Cambodia

Cambodian–Vietnamese War
Part of the Third Indochina War and the Cold War
Vietnamese soldiers entering Phnom Penh in January 1979
Date 30 April 1977 – 23 October 1991 (14 years, 5 months, 3 weeks and 2 days) Small scale fighting had occurred since May 1975 Full scale war took place between 25 December 1978 and 7 January 1979 (invasion of Democratic Kampuchea by Vietnamese forces until the fall of Phnom Penh) Location Cambodia, southern Vietnam, eastern Thailand Result Vietnamese military victory Removal of the Khmer Rouge from power End of the Cambodian Genocide Democratic Kampuchea replaced by People's Republic of Kampuchea Vietnamese occupation of Cambodia Continued fighting between various Cambodian factions Border conflicts between Vietnam and China and between Vietnam and Thailand
Belligerents
Vietnam FUNSK	Democratic Kampuchea
Post invasion:  Vietnam People's Republic of Kampuchea	Post invasion: CGDK: Khmer Rouge KPNLF FUNCINPEC  Thailand (border clashes)
Commanders and leaders
Lê Đức Anh Heng Samrin Hun Sen	Pol Pot Khieu Samphan Son Sann Dien Del Norodom Sihanouk
Strength
150,000–200,000 Vietnamese soldiers	1979: 73,000 1989: 30,000
Casualties and losses
1979–1989: 15,000–25,300 killed 30,000 wounded	1979: 15,000 killed Total: 50,000+ killed
100,000+ civilians killed (excluding famine)

Vietnamese military victory

 Thailand (border clashes)

The Cambodian–Vietnamese War was an armed conflict between the Socialist Republic of Vietnam and Democratic Kampuchea. The war began with isolated clashes along the land and maritime boundaries of Vietnam and Kampuchea between 1975 and 1977, occasionally involving division-sized military formations. On 25 December 1978, Vietnam launched a full-scale invasion of Kampuchea and subsequently occupied the country and removed the Khmer Rouge government from power.

During the Vietnam War, Vietnamese and Khmer Rouge communists had formed an alliance to fight U.S.-backed regimes in their respective countries. Despite their open display of cooperation with the Vietnamese, the Khmer Rouge leadership feared that the Vietnamese communists were scheming to form an Indochinese federation with Vietnam as the dominant force in the region. In order to preempt an attempt by the Vietnamese to dominate them, the Khmer Rouge leadership began purging Vietnamese-trained personnel within their own ranks as the Lon Nol regime capitulated in 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 Phú Quốc. 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.

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Wikipedia