...Border clashes with Vietnam led to Kampuchea cutting off diplomatic relations with its neighbor in late 1977. The Vietnamese, who stepped up their border attacks, encouraged Kampuchean rebels to overthrow the Pol Pot regime. In late 1978, about 200,000 Vietnamese troops invaded and occupied Kampuchea, whose capital, Phnom Penh, fell on January 9, 1979; Heng Samrin (1931-), a dissident Khmer Rouge, became president of a Vietnamese-supported government. Khmer Rouge loyalists, however, continued to fight in rural areas and jungles, attacking enemy supply lines and avoiding direct, large-scale battles. Pol Pot, who had fled to the northwest jungle, was recognized by the United States and China, both of which refused to accept Soviet-backed Vietnamese aggression. In 1982, three main anti-Vietnamese Khmer forces united in a coalition to oust the Vietnamese military occupiers of their country, while Prince Norodom Sihanouk (1922-), the country's former head of state, formed a coalition government-in-exile (which included Pol Pot's Khmer Rouge), recognized by the United Nations and available to replace the Vietnamese-aided regime. The Vietnamese launched strong attacks on the camps of Khmer "freedom fighters" along the Thai-Kampuchean border; in 1984, Vietnam showed increasing dependence on Soviet aid to combat the stiff guerrilla resistance. In 1987-88, Sihanouk met several times with Phnom Penh leaders without success. Urged by the Soviets, Vietnam began to withdraw some of its 140,000-man occupying arm, with plans to be completely out by 1990. The Khmer Rouge (40,000 strong) tried to regain territory, while another rebel force, the noncommunist Khmer People's National Liberation Front (KPNLF), had internal strife. In 1989, the Phnom Penh regime renamed the country Cambodia, and Vietnam sped up its withdrawal of troops. A UN-brokered peace agreement was signed in Paris on October 23, 1991, by the four Khmer factions -- Sihanoukists, KPNLF, Khmer Rouge, and the Phnom Penh government -- and ministers of 19 other countries that participated in peace talks. Disarming of some of the factions then began under the UN Transitional Authority in Cambodia (UNTAC), which also aided in the return of 375,000 refugees along the border of Thailand. In 1991, Sihanouk returned to Phnom Penh and became the elected president, replacing Heng Samrin...