The people given the most power in the new government were the largely illiterate rural Cambodians who had fought alongside the Khmer Rouge in the civil war. DK leaders severely restricted freedom of speech, movement, and association, and forbade all religious practices. The regime controlled all communications along with access to food and information. Former city dwellers, now called "new people," were particularly badly treated. The Khmer Rouge killed intellectuals, merchants, bureaucrats, members of religious groups, and any people suspected of disagreeing with the party. Millions of other Cambodians were forcibly relocated, deprived of food, tortured, or sent into forced labor.

The Khmer (Cambodians) account for the vast majority of the total population. This has produced a homogeneity that is unique in Southeast Asia and has encouraged a strong sense of national identity. Other traditional ethnic groups included the Chinese, Vietnamese, Cham-Malays, various tribal peoples, and Europeans. With the upheavals of the 1970s, the number of European residents declined precipitously, while many Chinese and local Vietnamese survivors emigrated overseas.