People with associations to the Vietnamese, whether that be former links with the communist movement there or just being an ethnic Vietnamese, were targeted by the Communist Party of Kampuchea (CPK).

While the statistic of 100% naturally involves a margin of error, it is certainly the case that most Vietnamese that remained in the country after the revolution in 1975 died in the four years the regime remained in power.

There are a few different reasons for this. First, it should be pointed out that the Khmer and the Vietnamese are, for lack of a better phrase, ‘hereditary enemies’. Folk lore and stories passed down from generations to the next detail atrocities by the Vietnamese or infer their desire to ‘take over’ Cambodia.

During the Cold War, the North Vietnamese helped train the Cambodian communists who would become the Khmer Rouge, while Sihanouk tried to appease them by allowing them to inhabit ‘sanctuaries’ along the border for their attacks on the South. After 1973 the Khmer Rouge looked to ‘stand on their own feet’, and lessened the influence of the Vietnamese in their movement. This sometimes took the form of purging cadre who had been trained by the Vietnamese.

Meanwhile, once the coup which had removed Sihanouk from power in 1970, the new leaders of Cambodia began campaigns of ethnic cleansing against the Vietnamese in Cambodia. Thousands were killed or fled back to Vietnam. By 1975 their numbers were relatively few - just 20,000 or so.

The Khmer Rouge moved toward eliminating the remaining Vietnamese for a couple of reasons; the new nation of Democratic Kampuchea was intended to be inhabited by ‘Kamoucheans’, and one official statistic claimed that less than 1% of the country was made up of ethnic minorities (it was closer to 20%). So there is an element of ethnic cleansing involved.

The second aspect relates to the war that broke out between the countries between 1975-79. Basically any Vietnamese were thought to be enemies of the party and were executed, including massacres of Vietnamese villagers across the border or Eastern Zone cadre thought to be suspicious/traitorous to the leaders in Phnom Penh.

Stats from Kiernan: The Pol Pot Regime Other sources include Henry Kamm’s Report From. Stricken Land and Philip Short’s Pol Pot: History of a Nightmare.