French Protectorate of Cambodia in the context of "Fall of Phnom Penh"

Cambodia, officially the Kingdom of Cambodia, is a country in Mainland Southeast Asia. It is bordered by Thailand to the northwest, Laos to the north, and Vietnam to the east, and has a coastline along the Gulf of Thailand in the southwest. It spans an area of 181,035 square kilometres (69,898 square miles), dominated by a low-lying plain and the confluence of the Mekong river and Tonlé Sap, Southeast Asia's largest lake. It is dominated by a tropical climate. Cambodia has a population of about 17 million people, the majority of which are ethnically Khmer. Its capital and most populous city is Phnom Penh, followed by Siem Reap and Battambang.

In 802 AD, Jayavarman II declared himself king, uniting the warring Khmer princes of Chenla under the name "Kambuja". This marked the beginning of the Khmer Empire. The Indianised kingdom facilitated the spread of first Hinduism and then Buddhism to Southeast Asia and undertook religious infrastructural projects throughout the region, the most famous of which is Angkor Wat. In the 15th century, it began a decline in power until, in 1863, Cambodia became a French protectorate. Following Japanese occupation during World War II, Cambodia declared independence from France in 1953. The Vietnam War embroiled the country in civil war during the 1960s, culminating in a 1970 coup which installed the US-aligned Khmer Republic and the takeover of the communist Khmer Rouge in 1975. The Khmer Rouge ruled the country and carried out the Cambodian genocide from 1975 until 1979, until they were ousted during the Cambodian–Vietnamese War. Peace was restored by the 1991 Paris Peace Accords and subsequent United Nations peacekeeping mission, establishing a new constitution, holding the 1993 general election, and ending long-term insurgencies. The 1997 coup d'état consolidated power under Prime Minister Hun Sen and the Cambodian People's Party (CPP).

The Nguyễn dynasty (Vietnamese: Nhà Nguyễn or Triều Nguyễn, chữ Nôm: 茹阮, chữ Hán: 朝阮) was the last Vietnamese dynasty, preceded by the Nguyễn lords and ruling unified Vietnam independently from 1802 until the start of the French protectorate in 1883. Its emperors were members of the House of Nguyễn Phúc. During its existence, the Nguyễn empire expanded into modern-day Southern Vietnam, Cambodia, and Laos through a continuation of the centuries-long Nam tiến and Siamese–Vietnamese wars. With the French conquest of Vietnam, the Nguyễn dynasty was forced to give up sovereignty over parts of Southern Vietnam to France in 1862 and 1874, and after 1883 the Nguyễn dynasty only nominally ruled the French protectorates of Annam (Central Vietnam) as well as Tonkin (Northern Vietnam). Backed by Imperial Japan, in 1945 the last Nguyễn emperor Bảo Đại abolished the protectorate treaty with France and proclaimed the Empire of Vietnam for a short time until 25 August 1945.

The House of Nguyễn Phúc established control over large amounts of territory in Southern Vietnam as the Nguyễn lords (1558–1777, 1780–1802) by the 16th century before defeating the Tây Sơn dynasty and establishing their own imperial rule in the 19th century. The dynastic rule began with Gia Long ascending the throne in 1802, after ending the previous Tây Sơn dynasty. The Nguyễn dynasty was gradually absorbed by France over the course of several decades in the latter half of the 19th century, beginning with the Cochinchina Campaign in 1858 which led to the occupation of the southern area of Vietnam. A series of unequal treaties followed; the occupied territory became the French colony of Cochinchina in the 1862 Treaty of Saigon, and the 1863 Treaty of Huế gave France access to Vietnamese ports and increased control of its foreign affairs. Finally, the 1883 and 1884 Treaties of Huế divided the remaining Vietnamese territory into the protectorates of Annam and Tonkin under nominal Nguyễn Phúc rule. In 1887, Cochinchina, Annam, Tonkin, and the French Protectorate of Cambodia were grouped together to form French Indochina.

Pol Pot (born Saloth Sâr; 25 May 1925 – 15 April 1998) was a Cambodian politician, revolutionary, and dictator who ruled the communist state of Democratic Kampuchea from 1975 until his overthrow in 1979. During his reign, his administration oversaw mass atrocities and he is widely believed to be one of the most brutal despots in modern world history. Ideologically a Maoist and Khmer ethnonationalist, Pot was a leader of Cambodia's Communist movement, known as the Khmer Rouge, from 1963 to 1997. He served as General Secretary of the Communist Party of Kampuchea from 1963 to 1981, during which Cambodia was converted into a one-party state. Between 1975 and 1979, the Khmer Rouge perpetrated the Cambodian genocide, in which an estimated 1.5–2 million people died—approximately one-quarter of the country's pre-genocide population. In December 1978, Vietnam invaded Cambodia to remove the Khmer Rouge from power. Within two weeks Vietnamese forces occupied most of the country, ending the genocide and establishing a new Cambodian government, with the Khmer Rouge restricted to the rural hinterlands in the western part of the country.

Born to a prosperous farmer in Prek Sbauv, French Cambodia, Pol Pot was educated at some of Cambodia's most elite schools. Arriving in Paris in October 1949 on an academic scholarship, he later joined the French Communist Party in 1951 while studying at École française de radioélectricité. Returning to Cambodia in 1953, he involved himself in the Khmer Viet Minh organisation and its guerrilla war against King Norodom Sihanouk's newly independent government. Following the Khmer Viet Minh's 1954 retreat into North Vietnam, Pol Pot returned to Phnom Penh, working as a teacher while remaining a central member of Cambodia's Marxist–Leninist movement. In 1959, he helped formalise the movement into the Kampuchean Labour Party, which was later renamed the Communist Party of Kampuchea (CPK). To avoid state repression, in 1962 he relocated to a jungle encampment and in 1963 he became the CPK's leader. In 1968, he relaunched the war against Sihanouk's government. After Lon Nol ousted Sihanouk in a 1970 coup, Pol Pot's forces sided with the deposed leader against the new government, which was bolstered by the United States military. Aided by the Viet Cong militia and North Vietnamese troops, Khmer Rouge forces advanced and controlled all of Cambodia by 1975.

The Japanese occupation of Cambodia (Khmer: ការត្រួតត្រារបស់ជប៉ុននៅកម្ពុជា) was the period of Cambodian history during World War II when the Kingdom of Cambodia was occupied by the Japanese. Vichy France, which was a client state of Germany, nominally maintained the French protectorate over Cambodia and other parts of Indochina during most of the Japanese occupation. This territory of Cambodia was reduced, by concessions to Thailand after the Franco-Thai War, so that it did not include Stung Treng Province, Battambang Province, and Siem Reap Province.

The Japanese occupation in Cambodia lasted from 1941 to 1945 and, in general, the Cambodian population escaped the brutalities inflicted on civilians by the Japanese occupiers in other countries of Southeast Asia. After the nominal French Indochina colonial government was overthrown in 1945, Cambodia became a pro-Tokyo puppet state until the surrender of Japan.