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 led to the overthrow of Norodom Sihanouk's government and the subsequent abolition of the federalist Cambodian monarchy in favour of a centralised republic. After the coup, Sihanouk fled to Pyongyang and later Beijing in exile.
The main cause of the coup was Norodom Sihanouk's tolerance of North Vietnamese military activity within Cambodia's borders; communist North Vietnam and its Viet Cong 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.
After Chief of State Sihanouk was overthrown on 18 March 1970, the Kingdom of Cambodia became a republic on 9 October, officially removing Queen Sisowath Kossamak. The character of the new regime was far-right and militaristic, and was also marked by massacres of Vietnamese Cambodians. Diplomatically, right before Sihanouk was overthrown, the Kingdom of Cambodia under Prime Minister Lon Nol ended its covert cooperation with North Vietnam. Following the removal of Sihanouk, the Kingdom of Cambodia and later the Khmer Republic had aligned themselves with South Vietnam (Republic of Vietnam) in the ongoing Vietnam War. The Khmer Republic promulgated its own constitution in 1972. It was opposed within the Cambodian borders by the National United Front of Kampuchea (Front uni national de Kampuchéa, FUNK), a relatively broad alliance between Sihanouk, his supporters, and the Communist Party of Kampuchea.
The insurgency itself was conducted by the CPNLAF, the Cambodian People's National Liberation Armed Forces: they belonged to the communist Khmer Rouge and were backed by both the North Vietnamese Army (PAVN) and the Viet Cong, who occupied parts of Cambodia as part of their ongoing war against South Vietnam and allies.
Despite the large quantities of military and financial aid from the United States, the Khmer National Armed Forces (Forces armées nationales khmères, or FANK) were poorly trained and unable to defeat either the CPNLAF or the Vietnamese forces of the PAVN and the Viet Cong. The Republic eventually fell on 17 April 1975, when the Khmer Rouge took Phnom Penh and briefly restored the Kingdom of Cambodia before renaming itself "Democratic Kampuchea" on 5 January 1976.
Sihanouk himself claimed that the coup was the result of an alliance between his longstanding enemies, the exiled right-wing nationalist Son Ngoc Thanh, the politician Prince Sisowath Sirik Matak (depicted by Sihanouk as a disgruntled rival claimant to the Cambodian throne) and the CIA, who wished to install a more US-friendly regime. There is in fact little if any evidence of CIA involvement in the coup, although it seems that sections of the US military establishment – notably the Army Special Forces – may have had some involvement in terms of offering support and training to the plotters after being approached by Lon Nol.
While Sihanouk was out of the country on a trip to France, anti-Vietnamese rioting took place in Phnom Penh, during which the North Vietnamese and Viet Cong embassies were sacked. It seems likely that this rioting was at least tolerated, and possibly actively organised, by Lon Nol, the Prime Minister, and his deputy Prince Sirik Matak. On 12 March, the prime minister closed the port of Sihanoukville – through which weapons were being smuggled to the Viet Cong – to the North Vietnamese and issued an impossible ultimatum to them. All PAVN/Viet Cong forces were to withdraw from Cambodian soil within 72 hours (on 15 March) or face military action.
Despite these actions, which directly contradicted Sihanouk's policy of partial tolerance of North Vietnamese activity, it appears that Lon Nol himself had great personal reluctance to depose the Head of State: he initially may merely have wanted Sihanouk to apply more pressure to the North Vietnamese. He initially refused to commit to the plan; to convince him, Sirik Matak – who appears to have had a coup in mind from the start – played him a tape-recorded press conference from Paris, in which Sihanouk threatened to execute them both on his return to Phnom Penh. However, the Prime Minister remained uncertain, with the result that Sirik Matak, accompanied by three army officers, compelled a weeping Lon Nol to sign the necessary documents at gunpoint.
A vote was taken in the National Assembly on 18 March under the direction of In Tam, in which Sihanouk was stripped of his power: Lon Nol assumed the powers of the Head of State on an emergency basis. On 28 and 29 March there were large-scale popular demonstrations in favour of Sihanouk in several provincial cities, but Lon Nol's forces suppressed them with great brutality, causing several hundred deaths. Lon Nol's brother Lon Nil was among a number of government officials who were murdered by demonstrators.
Following the coup, North Vietnam and the Viet Cong advised Cambodia on 25 March 1970 that they were recalling all their diplomats from the country. In May 1970, North Vietnam withdrew its recognition of Cambodia, while Cambodia withdrew its recognition of the Viet Cong and re-established diplomatic relations with South Vietnam. Cambodia and South Vietnam would subsequently exchange ambassadors.
Declaration of the Khmer Republic and the formation of the FANK
The most significant immediate effect of the coup was the Cambodian campaign of April–July 1970, in which the South Vietnamese Army (ARVN), backed by US troops, entered eastern Cambodia to attack North Vietnamese and Viet Cong forces operating there. Despite this assault, many of the communist forces escaped westward, deeper into Cambodia, or to the rural areas of the north-east, where they would provide support for the insurgency against Lon Nol.
Lon Nol's immediate reaction was to condemn the action as a violation of Cambodian territory. He later informed Alexander Haig that his country had been placed in serious danger as a result. When Haig told him that American ground forces would not be used to assist the Cambodian army, and that (in accordance with the Nixon Doctrine) a programme of aid would be given instead, Lon Nol openly wept.
On 9 October Sihanouk was condemned to death in absentia by a military court; his mother, Queen Kossamak – the symbolic representative of the monarchy under Sihanouk's regime – was placed under house arrest, and his wife Monique was sentenced to life imprisonment. The new regime simultaneously declared the Khmer Republic, and a new constitution was eventually to be adopted in 1972. Sihanouk, in the meantime, had formed GRUNK, a Beijing-based government-in-exile incorporating the communists and dedicated to the Republic's overthrow; he declared Lon Nol to be a "complete idiot" and characterised Sirik Matak as "nasty, perfidious, a lousy bastard".
The relatively small Royal Khmer Armed Forces (FARK), which at the time of the coup had around 35,000 troops (in accordance with Sihanouk's stated policy of neutrality), was greatly expanded. Reorganising as the Khmer National Armed Forces (FANK), the republican military had grown to around 150,000 men as early as the end of 1970, mainly through voluntary enlistment as Lon Nol sought to capitalise on a wave of anti-Vietnamese sentiment. The regime's policies also carried out mass killings of Vietnamese Cambodians. The US also implemented its programme of structured military aid and assistance in training, and flew in several thousand Khmer Serei and Khmer Kampuchea Krom militia, trained in South Vietnamese bases. The Joint Chiefs insisted on massive expansion of the FANK to over 200,000 men, despite concerns at the severe negative effect this would have on Cambodia's economy, while the Military Equipment Delivery Team, led by General Theodore C. Mataxis, demanded the 'Americanisation' of the army's French-influenced internal structures, in spite of the chaos this caused in the supply chain.