Pol Pot transformed Cambodia into a one-party state called Democratic Kampuchea. Seeking to create an agrarian socialist society that he believed would evolve into a communist society, Pol Pot's government forcibly relocated the urban population to the countryside to work on collective farms. Pursuing complete egalitarianism, money was abolished and all citizens were made to wear the same black clothing. Pol Pot was a driving force behind the Cambodian genocide, the systematic persecution and killing of Cambodians that the Khmer Rouge regarded as enemies. The genocide, coupled with malnutrition and poor medical care, killed between 1.5 and 2 million people, approximately a quarter of Cambodia's population. Repeated purges of the CPK generated growing discontent; by 1978 Cambodian soldiers were mounting a rebellion in the east. After several years of border clashes, the newly unified Vietnam invaded Cambodia in December 1978, toppling Pol Pot and installing a rival Marxist–Leninist government in 1979. The Khmer Rouge retreated to the jungles near the Thai border, from where they continued to fight. In declining health, Pol Pot stepped back from many of his roles in the movement. In 1998 the Khmer Rouge commander Ta Mok placed Pol Pot under house arrest, shortly after which he died.