Fall of Phnom Penh in the context of "Khieu Samphan"

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).

Khmer Rouge is the name that was popularly given to members of the Communist Party of Kampuchea (CPK), and by extension to Democratic Kampuchea, which ruled Cambodia between 1975 and 1979. The name was coined in the 1960s by Norodom Sihanouk to describe his country's heterogeneous, communist-led dissidents, with whom he allied after the 1970 Cambodian coup d'état.

The Kampuchea Revolutionary Army was slowly built up in the forests of eastern Cambodia during the late 1960s, supported by the People's Army of Vietnam, the Viet Cong, the Pathet Lao, and the Chinese Communist Party (CCP). Although it originally fought against Sihanouk, the Khmer Rouge changed its position and supported Sihanouk following the CCP's advice after he was overthrown in a 1970 coup d'état by Lon Nol who established the pro-American Khmer Republic. Despite a massive American bombing campaign (Operation Freedom Deal) against them, the Khmer Rouge won the Cambodian Civil War when they captured the Cambodian capital and overthrew the Khmer Republic in 1975. Following their victory, the Khmer Rouge—who were led by Pol Pot, Nuon Chea, Ieng Sary, Son Sen, and Khieu Samphan—immediately set about forcibly evacuating the country's major cities. In 1976, they renamed the country Democratic Kampuchea.

The Cambodian genocide was the systematic persecution and killing of Cambodian citizens by the Khmer Rouge under the general secretaryship of Pol Pot. It resulted in the deaths of 1.5 to 2 million people from 1975 to 1979, nearly 25% of Cambodia's population in 1975 (c. 7.8 million).

Pol Pot and the Khmer Rouge were supported for many years by the Chinese Communist Party (CCP), led by Chairman Mao Zedong; it is estimated that at least 90% of the foreign aid which the Khmer Rouge received came from China, including at least US$1 billion in interest-free economic and military aid in 1975 alone. After it seized power in April 1975, the Khmer Rouge wanted to turn the country into an agrarian socialist republic, founded on the policies of ultra-Maoism and influenced by the Cultural Revolution. Pol Pot and other Khmer Rouge officials met with Mao in Beijing in June 1975, receiving approval and advice, while high-ranking CCP officials such as Politburo Standing Committee member Zhang Chunqiao later visited Cambodia to offer help. To fulfill its goals, the Khmer Rouge emptied the cities and marched Cambodians to labor camps in the countryside, where mass executions, forced labor, physical abuse, torture, malnutrition, and disease were rampant. In 1976, the Khmer Rouge renamed the country Democratic Kampuchea.

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.

Founded in 1372, Phnom Penh succeeded Angkor Thom as the national capital in 1434 following the fall of Angkor, and remained so until 1497. It regained its capital status during the French colonial era. It underwent a period of investment and modernization during Cambodia's independence period, earning the nickname the "Pearl of Asia" for its colonial French, New Khmer and Art Deco architecture. The city's population swelled in the 1960s and 1970s as refugees fled from civil war and American bombing during the Vietnam War. Phnom Penh's entire population was forcibly evacuated in 1975 by the Khmer Rouge, and faced persecution, forced labour and genocide. Phnom Penh remained largely uninhabited during the Democratic Kampuchea era until Vietnam-backed forces took the city in 1979. The city was reconstructed and infrastructure improved in the modern era with the support of international investment and aid. By 2019, it was home to more than 2 million people, approximately 14% of the Cambodian population.

The French protectorate of Cambodia (Khmer: ប្រទេសកម្ពុជាក្រោមអាណាព្យាបាលបារាំង; French: Protectorat français du Cambodge) refers to the Kingdom of Cambodia when it was a French protectorate within French Indochina, a collection of Southeast Asian protectorates within the French colonial empire. The protectorate was established in 1863 when the Cambodian King Norodom requested the establishment of a French protectorate over his country, meanwhile Siam (modern Thailand) renounced suzerainty over Cambodia and officially recognised the French protectorate on Cambodia.

Cambodia was integrated into the French Indochina union in 1887 along with the French colonies and protectorates in Laos and Vietnam (Cochinchina, Annam, and Tonkin). In 1947, Cambodia was granted self-rule within the French Union and had its protectorate status removed in 1949. Cambodia later gained independence. The day was celebrated as Independence Day on 9 November 1953 led by King Sihanouk and continued to rule as the leader of the nation until he was overthrown in 1970 by the US-led Khmer Republic of Lon Nol in a coup d'état before the rise of Angkar and the Khmer Rouge coming to power on 17 April 1975, following the Fall of Phnom Penh and the end of the Cambodian Civil War.

The Kingdom of Cambodia, also known as the First Kingdom of Cambodia, and commonly referred to as the Sangkum period, refers to Norodom Sihanouk's first administration of Cambodia, lasting from the country's independence from France in 1953 to a military coup d'état in 1970. Sihanouk continues to be one of the most controversial figures in Southeast Asia's turbulent and often tragic postwar history. From 1955 until 1970, Sihanouk's Sangkum was the sole legal party in Cambodia. After the 1970 coup, the semi-official name of Cambodia was State of Cambodia, it became a transitional government under a military dictatorship of Prime Minister Lon Nol against the Khmer Rouge and North Vietnamese.

Following the end of World War II, France restored its colonial control over Indochina but faced local resistance against their rule, particularly from Communist guerilla forces. On 9 November 1953, Cambodia achieved independence from France under Norodom Sihanouk but still faced resistance from Communist groups such as United Issarak Front. As the Vietnam War escalated, Cambodia sought to retain its neutrality but in 1965, North Vietnamese soldiers were allowed to set up bases and in 1969, the United States began a bombing campaign against North Vietnamese soldiers in Cambodia. The Cambodian monarchy was abolished in a coup on October 9, 1970 headed by Prime Minister Lon Nol, who established the Khmer Republic which lasted until the Fall of Phnom Penh to the Khmer Rouge led by Angkar ("Organization") when it came to power on 17 April 1975.

Democratic Kampuchea was the official name of the Cambodian state from 1976 to 1979, under the general secretaryship of Pol Pot and the Communist Party of Kampuchea (CPK), commonly known as the Khmer Rouge. The Khmer Rouge's capture of the capital Phnom Penh in 1975 effectively ended the United States-backed Khmer Republic under Prime Minister-later President Lon Nol.

From 1975 to 1979, the Khmer Rouge's one-party regime killed millions of its own people through mass executions, forced labour, and starvation, in an event which has come to be known as the Cambodian genocide. The killings ended when the Khmer Rouge were ousted from Phnom Penh by the People's Army of Vietnam (PAVN). The Khmer Rouge subsequently established a government-in-exile in neighbouring Thailand and retained Kampuchea's seat at the United Nations (UN). In response, Vietnamese-backed communists created a rival government, the People's Republic of Kampuchea, but failed to gain international recognition.

Year Zero (Khmer: ឆ្នាំសូន្យ, Chhnăm Sony [cʰnam soːn]) is an idea put into practice by Pol Pot in Democratic Kampuchea that all culture and traditions within a society must be completely destroyed or discarded and that a new "revolutionary" culture must replace it starting from scratch. In this sense, all of the history of a nation or a people before Year Zero would be largely deemed irrelevant, because it would ideally be purged and replaced from the ground up.

The first day of "Year Zero" was declared by Angkar and the Khmer Rouge on 17 April 1975 upon their takeover of Cambodia to signify a rebirth of Cambodian history. Adopting the term as an analogy to the "Year One" of the French Revolutionary Calendar, Year Zero was, in effect, an attempt by the Khmer Rouge to erase history and reset Cambodian society, removing any vestiges of the past.

Lon Nol (Khmer: លន់ នល់, also លន់ ណុល; 13 November 1913 – 17 November 1985) was a Cambodian military officer and politician who served as Prime Minister of Cambodia twice (1966–1967; 1969–1971), as well as serving repeatedly as defence minister and provincial governor. As a right-wing nationalist, he led the military coup of 1970 against Prince Norodom Sihanouk, abolished the monarchy, and established the short-lived Khmer Republic. Constitutionally a semi-presidential republic, Cambodia was de facto governed under a military dictatorship. He was the commander-in-chief of the Khmer National Armed Forces during the Cambodian Civil War and became President of the Khmer Republic on 10 March 1972. On 1 April 1975, as the only president of the republic 16 days before Angkar and the Khmer Rouge captured Phnom Penh, Lon Nol fled to Indonesia and later the United States, first to Hawaii and then to California, where he remained until his death in 1985.