Third Indochina War: Cambodian–Vietnamese War: Phnom Penh falls to the advancing Vietnamese troops, driving out Pol Pot and the Khmer Rouge.

The Sino-Vietnamese War was a brief conflict that occurred in early 1979 between China and Vietnam. China launched an offensive ostensibly in response to Vietnam's invasion and occupation of Cambodia in 1978, which ended the rule of the Chinese-backed Khmer Rouge. The conflict lasted for about a month, with China withdrawing its troops in March 1979.

The Cambodian–Vietnamese War was an armed conflict between the Khmer Rouge-led Democratic Kampuchea and the Socialist Republic of Vietnam. 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.

Phnom Penh is the capital and most populous city of Cambodia. It has been the national capital since 1865 and has grown to become the nation's primate city and its political, economic, industrial, and cultural centre. The city's name derives from Wat Phnom, a Buddhist temple, and Lady Penh, the city's founder. It sits at the confluence of the Tonlé Sap and Mekong rivers, and is the start of the Bassac River. It is also the seat of Cambodia's monarchy, based at the Royal Palace.

Vietnam, officially the Socialist Republic of Vietnam (SRV), is a country at the eastern edge of mainland Southeast Asia, with an area of about 331,000 square kilometres (128,000 sq mi) and a population of over 100 million, making it the world's fifteenth-most populous country. One of two communist states in Southeast Asia, Vietnam shares land borders with China to the north, and Laos and Cambodia to the west. Its capital is Hanoi and its largest city is Ho Chi Minh City.