The Khmer Rouge army was slowly built up in the jungles of Eastern Cambodia during the late 1960s , supported by the North Vietnamese army , the Viet Cong and the Pathet Lao . Despite a massive American bombing campaign against them , the Khmer Rouge won the Cambodian Civil War when in 1975 they captured the Cambodian capital and overthrew the government of the Khmer Republic . Following their victory , the Khmer Rouge led by Pol Pot , Nuon Chea , Ieng Sary , Son Sen and Khieu Samphan renamed the country as Democratic Kampuchea and immediately set about forcibly evacuating the country 's major cities . The regime murdered hundreds of thousands of their perceived political opponents . Ultimately , the Cambodian genocide led to the deaths of 1.5 to 3 million people , around 25 % of Cambodia 's population
Cambodian genocide
Cambodian genocide
Khmer Rouge