Cambodia: U.S. bombing, civil war, & Khmer Rouge

Part One: U.S. Bombing & Civil War | Fatalities | Ending
Part Two: Khmer Rouge |Fatalities | Ending
Coding | Works Cited | Notes


From the start of the U.S. bombing campaign in Cambodia (1965) until the Vietnamese army overthrew the Khmer Rouge regime (1979), the country suffered annual tolls estimated to be in excess of 5,000 civilian casualties—thereby qualifying the entire period as a single case for the purposes of this study. Over the 14-year period, the vast majority of civilian deaths were caused by the Khmer Rouge regime, but significant numbers of civilian casualties also resulted from earlier violence during the U.S. bombing and civil war that brought the Khmer Rouge to power. To capture the changing dynamics over time, we have separated the case study below into two periods, the U.S. bombing and civil war, and the Khmer Rouge regime.

Part One: U.S. Bombing & Civil War

Between 1965 and 1975, the expansion of the Vietnam War into Cambodia aggravated and radicalized internal Cambodian political disputes. These disputes readily became armed contests characterized by shifting alliances, regional struggles for dominance (including the US, Soviet Union, China and Vietnam), and Cambodian efforts to assert different varieties of militant nationalism (whether royalist, communist or otherwise). The result for civilians was devastating.

In 1965, Cambodia officially cut ties with the U.S., as Prince Sihanouk, the country’s head of state, tried, in his words, to maintain the country’s neutrality regarding the war in Vietnam. Nonetheless, his policies allowed Vietnamese communists to use border areas and the port of Sihanoukville. The U.S., under Lyndon Johnson’s administration, responded with targeted bombing of military installations and occasional attacks on Cambodian villages by South Vietnamese and American forces. Between 1965 and 1969, the U.S. bombed 83 sites in Cambodia. The pace of bombing increased in 1969, as U.S. B-52 carpet-bombing began, in support of the slow pullout of U.S. troops from Vietnam. Bombers targeted mobile headquarters of the South Vietnamese “Viet Cong” and the North Vietnamese Army in the Cambodian jungle.[i]

In March 1970, a coup was launched against Prince Sihanouk resulting in a new government with Lon Nol at the helm. The coup government made a drastic change in Cambodian policies, deciding to counter the North Vietnamese, in support of the South Vietnamese and U.S. forces. In May 1970, the US and South Vietnamese launched an offensive into Cambodia, with the aim of cutting off North Vietnamese supply routes. The Vietnamese Communists widened and intensified their actions in Cambodia as well, working with insurgent Cambodia communists.[ii] After the U.S. ground invasion failed to root out the Vietnamese communists, in December 1970, Nixon instructed his Secretary of State Henry Kissinger to order the Air Force to ignore restrictions limiting U.S. attacks to within 30 miles of the Vietnamese border, expanding the bombing areas. However, extensive bombing forced the Vietnamese communists further west and deeper into Cambodia, and ultimately radicalized Cambodian citizens against the government

An alliance of royalist, Cambodian and regional communist forces fought against the Lon Nol government, US and South Vietnamese forces, and, despite many internal rifts, expanded their areas of control quickly. By 1971, writes Kiernan, the Lon Nol government was secure only in the towns and their outskirts.[iii] As the allied Communist forces gained control of territory, the Communist Party of Cambodia (CPK) attempted to win over the Khmer soldiers fighting with the Vietnamese and to expel the Vietnamese forces. In some places, this effort resulted in heavy fighting between ostensible allies.[iv] As peace talks began in Paris, the CPK adamantly refused to participate in a negotiated solution.[v]

The final phase of the U.S. bombing campaign, from January to August 1973, aimed to halt the rapid advance of the Khmer Rouge on Phnom Penh, in response, the U.S. military escalated air raids that spring and summer with an unprecedented B-52 bombardment campaign that focused on the heavily populated areas around Phnom Penh, but which affected almost the entire country. The sum effect was that while the take-over of Phnom Penh was delayed, hard-liners within the CPK were strengthened, the populace further turned against the Lon Nol government, and the Communists’ recruitment efforts were facilitated.[vi]

After the U.S. bombing campaign ended, the civil war continued with the Communist forces making steady progress, despite fighting within their ranks and between groups.

U.S. Bombing
Our research indicted a rough low estimate of 250,000 people during this period.

Fatalities from U.S. bombing were concentrated during the period in which U.S. President Richard Nixon’s administration carpet-bombed eastern Cambodia from 1969 to 1973, although bombings and incursions into Cambodia by the U.S. began in 1965 under President Lyndon B. Johnson and ended in 1975 under President Gerald Ford. More than 10 percent of the U.S. bombing was indiscriminate.

Former National Security Adviser than Secretary of State, Henry Kissinger, an architect of US policy in Indochina, states in his book Ending the Vietnam War that the Historical Office of the U.S. Secretary of Defense gave him an estimate of 50,000 deaths in Cambodia due to the bombings from 1969-1973. The U.S. government released new information about the extent of the bombing campaign in 2000, leaving Owen and Kiernan to argue that the new evidence released by the U.S. government in 2000 support higher estimates.[vii] On the higher end of estimates, journalist Elizabeth Becker writes that “officially, more than half a million Cambodians died on the Lon Nol side of the war; another 600,000 were said to have died in the Khmer Rouge zones.”[viii] However, it is not clear how these numbers were calculated or whether they disaggregate civilian and soldier deaths. Others’ attempts to verify the numbers suggest a lower number. Demographer Patrick Heuveline[ix] has produced evidence suggesting a range of 150,000 to 300,000 violent deaths from 1970 to 1975.

In an article reviewing different sources about civilian deaths during the civil war, Bruce Sharp[x] argues that the total number is likely to be around 250,000 violent deaths. He argues that several factors support this range: 1) Interviews with survivors after the Khmer Rouge period who discussed when and how their family members were killed; 2) research by social scientists Steven Heder and May Ebihara, both of whom (separately) conducted extensive interviews with Cambodians; 3) adding information about the geography of conflict and variations in the intensity of the conflict; and 4) application of insights from documentation of the Vietnam War.

Sharp addresses some reasons why discrepancies may appear in various interview-based sources. First, there may be different perceptions about what is a “war-related” death that would inhibit assessment of increased mortality. Second, deaths calculated in relation to reporting by family members requires that a family member survive and bombs would have high clustering of mortality, potentially killing entire families. Third, the areas heavily targeted by the U.S. bombing campaign were subsequently heavily targeted by the Khmer Rouge, again, potentially leaving a gap in reporting if no family members survived.


US bombing of Cambodia came to a halt in August of 1973 when the US Congress legislated its conclusion, following the signing of a peace agreement between the US and North Vietnamese. The Khmer Rouge and Lon Nol armies continued to fight for two more years until 1975 when Phnom Penh fell to the Khmer Rouge.

On April 17, 1975, the Khmer Rouge entered Phnom Penh and declared Day Zero, ousting the military regime and emptying the cities. The defeat of Lon Nol forces precipitated an end to civil war deaths, but the beginning of the Khmer Rouge’s purge of perceived enemies. The civil war ended when the Khmer Rouge decisively won, an “end” that served only as prelude to a more intensive period of targeting civilians.

Part II: the Khmer Rouge (1970-1979)


Once the Khmer Rouge (KR) took over the country, they began to implement radical plans to restructure society. Among the influences and populations targeted for elimination were: Buddhism; “foreign” influences (including targeting the urban, educated class); entire minority groups (the Chinese, Vietnamese, Muslim Cham, and Thai[xi]); as well as those Khmer who were deemed unfit as determined by an ever-widening criteria. The KR goal was to create an agrarian communist state by controlling family relations, restructuring agriculture, re-organizing the political, legal, and military institutions of the state, and collectivizing economic production and consumption—in short, to establish complete control over society.

The Khmer population was divided into “old citizens” – those who lived in KR zones before their 1975 victory and “new citizens” those who fell under their control thereafter.[xii] As Alex Hinton writes, “in the new revolutionary society, each person had to be reworked, like hot iron, in the flames of the revolution.”[xiii] However, despite the regime’s emphasis on targeting foreign elements in society, by the end of the conflict the majority of killing had been perpetrated by Khmer citizens against other Khmer citizens.[xiv] The lack of popular base for the KR and upheaval wrought by their policies required extensive use of lethal force to maintain control.[xv] Kiernan notes that the “most horrific slaughter was perpetrated in the last six months of the regime” in areas bordering Vietnam.[xvi]


Our research suggests a range of 650,000 – 1.4 million violent deaths between 1970-1979.

Many attempts have been made to count or estimate the scale of deaths under the KR.[xvii] While the KR officials claim that only around 20,000 civilians were killed, the true estimate likely falls somewhere between 1-3 million total deaths, with upper range estimates of those directly killed by the regime approaching 1 million.

Demographic analysis has been undertaken by many parties including the US Central Intelligence Agency[xviii] and a variety of historians.[xix] By estimating population numbers before and after the genocide and taking into account expected fertility rates, migration rates, and normal expected mortality rates, these demographic analyses attempt to calculate the excess mortality rate. One of the more thorough demographic studies, conducted by Patrick Heuveline, also attempts to separate out violent civilian deaths from a general increase in mortality caused by famine, disease, working conditions, or other indirect causes. He does so by grouping deaths within different age and sex brackets and analyzing treatment of these age and sex groups by the Khmer Rouge and violent regimes in general. His conclusion is that an average of 2.52 million people (range of 1.17-3.42 million) died as a result of regime actions between 1970 and 1979, with an average estimate of 1.4 million (range of 1.09-2.16 million) directly violent deaths.[xx]

Researchers have also attempted to estimate deaths attributable to the regime by interviewing segments of the Cambodian population and extrapolating this information to the wider population. Through this method, Cambodia scholar Ben Kiernan originally estimated that 1.5 million deaths resulted from the regime’s policies (his figure was later scaled up to 1,671,000)[xxi]. This figure amounts to a loss of 21% of the population[xxii]–approximately 15% of the rural population and 25% of the urban population[xxiii]–but includes both people who were violently killed and those that died of starvation, overwork, and disease.[xxiv] As Ben Kiernan notes in his book, Milton Osborne valued the percentage of overall deaths that occurred as a result of execution to be 31 percent.[xxv] If this percentage is applied to Kiernan’s most recent estimate of overall deaths, then the number of violent deaths by execution is 539,032.

A much larger estimate of overall deaths was put forward by the People’s Republic of Kampuchea (PRK), the Vietnamese backed government that took control of Cambodia after Vietnam defeated the Khmer Rouge. In the early 1980s, the PRK attempted to quantify deaths by interviewing Cambodians at the household or village level throughout the country. They estimated that 3,314,768 people lost their lives under the KR.[xxvi] However, this figure has been criticized as an over-estimate resulting from the PRK’s methods, which did not take into account the fact that families may have been geographically dispersed during the period and also involved adding reported deaths to estimates from exhumed mass graves.

The Documentation Center of Cambodia (DC-Cam) with Craig Etcheson undertook a mass grave survey to estimate deaths by the KR. Although this method of estimation is complicated by the difficulty of determining cause and time of death, in 1999, DC-Cam estimated that their ongoing investigations had uncovered 20,492 mass graves containing the remains of roughly 1.1 million victims of KR government execution. Although larger than some other estimates, Etcheson argues that these numbers are plausible, given the nature of the mass grave and DC-Cam’s methods, which are more likely to produce an under-count of bodies rather than an over-estimate.[xxvii]


The KR initiated several attacks against Vietnam, despite its comparative weaknesses. Several skirmishes occurred along the Cambodian-Vietnamese border beginning in 1977, escalating to large-scale battles by early 1978.[xxviii] Purges of KR leadership also caused defectors to flee to Vietnam and request military assistance. In December of 1978, Vietnam broadcast that a Kampuchean Front for National Liberation had been established in “liberated Cambodian territory”. This announcement was followed by a second invasion on Christmas day of 1978.[xxix] In January of 1979, Vietnamese forces took control of the capital; Pol Pot and the remaining KR leadership fled to the Southwest of the country.[xxx] The Vietnamese capture of Phnom Penh and establishment of the People’s Republic of Kampuchea marked the end of mass atrocities in Cambodia.

International support for the KR continued long thereafter, both in the refugee camps in Thailand and in international diplomatic arenas. The KR, which separated itself from Vietnamese and Soviet influence, received backing from China, the U.S. and most western countries even after the end of the Cold War. The KR, for instance, held Cambodia’s seat at the UN until 1993, long after it had been defeated by Vietnam.

Armed groups composed of the remnants of the KR together with the FUNCINPEC and KPNLF forged a coalition in 1982 to continue to challenge the Vietnamese-backed state. The 1991 Paris Peace Accords, co-chaired by the Ministers of Foreign Affairs of France and Indonesia, four Cambodian parties, and the Secretary General of the United Nations, in addition to many national representatives, culminated in a final agreement signed by 19 governments. The agreement further established the United Nations Transitional Authority in Cambodia to implement the agreements, an ambitious mission with military, civil administration, human rights, policing, repatriation, rehabilitation, and electoral components. Elections were held in May 1993, and a new constitution was promulgated on 24 September 1993.


The long period of atrocities ended in international defeat of the primary perpetrators when the Vietnamese invasion overthrew the Khmer Rouge. We also code that initiator of atrocities period, the U.S. through the bombing campaign, was not the perpetrator who committed the most atrocities. Further, we note that there were multiple victim groups, to account for the different logics of targeting civilians.

Works Cited

Banister, Judith and Paige Johnson. 1993.”After the Nightmare: The Population of Cambodia,” in Genocide and Democracy in Cambodia: The Khmer Rouge, the United Nations and the International Community, ed. Ben Kiernan. New Haven, CT: Yale University Southeast Asia Studies.

Becker, Elizabeth. 1986. When the War Was Over: Cambodia and the Khmer Rouge Revolution. New York: Public Affairs.

Chandler, David. 2008. A History of Cambodia, 4th ed. Boulder, CO: Westview Press, 2008.

Etcheson Craig. 1984. The Rise and Demise of Democratic Kampuchea. Boulder, CO: Westview/Pinter.

Etcheson, Craig. 1999. “‘The Number’: Quantifying Crimes Against Humanity in Cambodia.” Mass Graves Study, Documentation Center of Cambodia.

Gottesman, Evan. 2003. After The Khmer Rouge: Inside the Politics of Nation Building. New Haven: Yale University Press.

Heuveline, Patrick. 1998. “’Between one ad three million’: Towards the demographic reconstruction of a decade of Cambodian history (1970 – 1979).” Population Studies 52: 49–65.

Hinton, Alexandar Laban. 2009. “Truth, Representation and the Politics of Memory after Genocide” in People of Virtue: Reconfiguring Religion, Power and Moral Order in Cambodia Today. ed. Alexandra Kent & David Chandler. Copenhagen: NIAS Press.

Hinton, Alexandar Laban. 2005. Why did they Kill?: Cambodia in the Shadow of Genocide. Berkeley and Los Angeles: University of California Press.

Kiernan, Ben. 1985. How Pol Pot Came to Power : A History of Communism in Kampuchea, 1930 – 1975. London: Verso.

Kiernan, Ben. 2008. The Pol Pot Regime: Race, Power, and Genocide in Cambodia under the Khmer Rouge, 1975-79, 2nd ed. New Haven, CT: Yale University Press.

Kiernan,Ben. 2009. “The Cambodian Genocide” in Century of Genocide, ed. Samuel Totten and William Parsons. Third Edition. New York: Routledge, 340 – 373.

Owen, Taylor and Ben Kiernan. 2006. “Bombs over Cambodia. The Walrus, October 2006, 62 – 69.

“Report of the Research Committee on Pol Pot’s Genocidal Regime.” 1983. Phnom Penh, Cambodia, July 25.

Sharp, Bruce. “Counting Hell” Available at: Accessed May 26, 2015.

Sliwinski, Marek. 1995. Le Génocide Khmer Rouge: un analyse démographique. Paris: Editions L’Harmattan.

U.S. Central Intelligence Agency. 1980. “Kampuchea: A Demographic Catastrophe.” Washington, DC, January 17.

Vickery, Michael. 1984. Cambodia 1975 – 1982. Boston, MA: South End Press.


[i] Owen and Kiernan 2006, 67.

[ii] Kiernan 1985, 305.

[iii] Kiernan 1985, 322.

[iv] Kiernan 1985, 342.

[v] Kiernan 1985, 343.

[vi] Etcheson. 1984, 119.

[vii] Owen and Kiernan 2006, 67.

[viii]Becker 1986, 170.

[ix] Heuveline 1998.

[x] Sharp.

[xi] Kiernan 2009, 346 – 347.

[xii] Kiernan 2009, 349.

[xiii] Hinton 2009, 63.

[xiv] Hinton 2005, 15.

[xv] Kiernan. 2009, 346.

[xvi] Kiernan, 2009, 349.

[xvii] Sharp.

[xviii] U.S. Central Intelligence Agency, 1980.

[xix] Sliwinski, 1995; Banister and Johnson, 1993; Vickery 1984.

[xx] Heuveline 1998.

[xxi] Kiernan 2008, 458.

[xxii] Kiernan 1996, 351

[xxiii] Kiernan 2009, 349.

[xxiv] Kiernan 1996, 351.

[xxv] Kiernan 1996, 456.

[xxvi] “Report of the Research Committee on Pol Pot’s Genocidal Regime” 1983.

[xxvii] Etcheson 1999

[xxviii] Etcheson 1999, 191.

[xxix] Gottesman 2003, 10 – 11.

[xxx] Chandler 2008.

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