Skulls of Khmer Rouge victims.
The Khmer Rouge killed an estimated 2 million Cambodians in a four year period. Deadly purges were conducted to "purify" the society. At the beginning they were aimed at the elements of the "old society": teachers, intellectuals, doctors, lawyers, wealthy people, Buddhist monks, police, former government officials and the educated. Towards 1967-68 the party became obssesed with the idea of enemies infiltrating into the party ranks and the bloody purges were carried out against party cadres.
Malnutrition and disease claimed a big number of deaths. The regions were given unrealistic quotas of rice that have to be sent to Phnom Penh and more often than not people would be left with no food in order to meet the quotas. Starvation along with lack of medical care (there were no trained people and no medicines) proved fatal, and by 1977 the country could not sustain itself due to the high percentage of death. However, delusions of grandeur of the regime led them to raid Vietnamese villages in order to gain control of the Mekong delta.
The poorly equipped Khmer troops were not match for the Vietnamese forces, and the results were catastrophic. Pol Pot responded with more purges within his party members and a number of them escaped to Vietnam. Amongst them was Heng Samrin, a militar whom the Vietnamese chose to replace Pol Pot, who was becoming a nuisance for them. In 1979 dissident Cambodians assisted by around 90,000 Vietnamese soldiers invaded Cambodia and Pol Pot's regime fleed to neighbouring Thailand. Despite the antivietnamese feelings of Cambodians, Vietnamese occupation was eagerly welcomed.