Lon Nol in the context of "Pol Pot"

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 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.

The 1970 Cambodian coup d'état (Khmer: រដ្ឋប្រហារឆ្នាំ១៩៧០, French: Coup d'État de 1970) was the removal of the Cambodian Chief of State, Prince Norodom Sihanouk, after a vote in the National Assembly on 18 March 1970. Emergency powers were subsequently invoked by the Prime Minister Lon Nol, who became effective head of state, and led ultimately to the removal of Queen Sisowath Kossamak and the proclamation of the Khmer Republic later that year. It is generally seen as a turning point in the Cambodian Civil War. No longer a monarchy, Cambodia was semi-officially called "État du Cambodge" (State of Cambodia) in the intervening six months after the coup, until the republic was proclaimed.

It also marked the change of Cambodia involvement in the Vietnam War, as Lon Nol issued an ultimatum to North Vietnamese forces to leave Cambodia.

The Khmer Republic (Khmer: សាធារណរដ្ឋខ្មែរ, Sathearonaroat Khmae; French: République khmère) was a Cambodian state under the United States-backed military dictatorship of Marshal Lon Nol from 1970 to 1975. Its establishment was formally declared on 9 October 1970, following the 18 March 1970 coup d'état which saw the overthrow of Norodom Sihanouk's government and the abolition of the Cambodian monarchy.

The main cause of the coup was Norodom Sihanouk's tolerance of North Vietnamese military activity within Cambodia's borders; Vietnamese communist forces had gained de facto control over vast areas of eastern Cambodia as a result. Another important factor was the dire state of the Cambodian economy, an indirect result of Sihanouk's policies of pursuing neutrality.

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.

Operation Freedom Deal was a military campaign led by the United States Seventh Air Force, taking place in Cambodia between 19 May 1970 and 15 August 1973. Part of the larger Vietnam War and the Cambodian Civil War, the goal of the operation was to provide air support and interdiction in the region. Launched by President Richard Nixon and orchestrated by United States Secretary of State Henry Kissinger, Deputy National Security Advisor Alexander Haig and Colonel Ray Sitton as a follow-up to the earlier ground invasion during the Cambodian Campaign, the initial targets of the operation were the base areas and border sanctuaries of the People's Army of Vietnam (PAVN) and the Viet Cong (VC).

As time went on, most of the bombing was carried out to support the Cambodian Government of Lon Nol in its struggle against the communist Khmer Rouge. The area in which the bombing took place was expanded to include most of the eastern one-half of Cambodia. The bombing was extremely controversial and led the U.S. Congress to pass the War Powers Resolution.