Đồng Tháp province in the context of "Vĩnh Long province"

The Cambodian–Vietnamese War was an armed conflict from 1978 to 1989 between the Khmer Rouge and Vietnam, and their respective allies. It began in December 1978, with a Vietnamese invasion of Cambodia which toppled the Khmer Rouge and ended in 1989 with the withdrawal of Vietnamese forces from Cambodia. This Cold War conflict was part of the Third Indochina War and Sino-Soviet split with the Soviet Union supporting Vietnam and China supporting the Khmer Rouge.

Despite both being communist, the alliance between the Communist Party of Vietnam and the Khmer Rouge broke down after both defeated Vietnamese and Cambodian anti-communist regimes respectively in the Vietnam War. As a result, the war was preceded by years of conflict between Vietnam and the Khmer Rouge, led by Pol Pot, when the Khmer Rouge ruled Democratic Kampuchea repeatedly invaded Vietnam, including massacres by the Khmer Rouge, notably the Ba Chúc massacre of over 3,000 Vietnamese civilians in April 1978. On 21 December 1978, the Vietnamese launched a limited offensive towards the town of Kratie. On 23 December 1978, 10 out of 19 divisions of the Khmer Rouge's Kampuchea Revolutionary Army opened fire along the border with Vietnam with the goal of invading the southwestern border provinces of Đồng Tháp, An Giang and Kiên Giang. On 25 December 1978, Vietnam supported Cambodian dissidents in exile and launched a full-scale invasion of Kampuchea, occupying the country in two weeks, capturing the capital Phnom Penh, and removing the Khmer Rouge government of the Communist Party of Kampuchea from power. In doing so, Vietnam put an ultimate stop to the Cambodian genocide which had killed between 1.2 and 2.8 million people or between 13 and 30 percent of the country's population since 1975. However, the Khmer Rouge regime maintained its membership in the United Nations and the war isolated Vietnam from the international community except the Eastern Bloc. The Vietnamese occupation caused discontent among Cambodians.

The Mekong Delta (Vietnamese: Đồng bằng Sông Cửu Long, lit. 'Nine Dragon River Delta' or simply Đồng Bằng Sông Mê Kông, 'Mekong River Delta'), also known as the South-western Region (Vietnamese: Tây Nam Bộ) or the Western Region (Vietnamese: Miền Tây), is the region in southwestern Vietnam where the Mekong River approaches and empties into the sea through a network of distributaries. The Mekong delta region encompasses a large portion of south-western Vietnam, of an area of over 40,500 km (15,600 sq mi). The size of the area covered by water depends on the season. Its wet coastal geography makes it an important source of agriculture and aquaculture for the country.

The delta has been occupied as early as the 4th century BC. As a product of Khmer, Vietnamese, Chinese, and French settlement in the region, the delta and its waterways have numerous names, including the Khmer term Bassac to refer to the lower basin and the largest river branch flowing through it. After the 1954 Geneva Conference, Vietnam was split into two with South Vietnam inheriting the southern half of Vietnam becoming the State of Vietnam and eventually the Republic of Vietnam, also known as South Vietnam, with their own administrative states (see Category:Provinces of South Vietnam). After 1975, the Mekong Delta ceased being a part of the Republic of Vietnam, succeeded by the current Vietnamese nation. The region comprises 4 provinces: Đồng Tháp, An Giang, Vĩnh Long, and Cà Mau, along with the province-level municipality of Cần Thơ.