Returning to Cambodia after visits to Moscow and Peking, Prince Norodom Sihanouk is ousted as Cambodian chief of state in a bloodless coup by pro-western Lt. Gen. Lon Nol, premier and defense minister, and First Deputy Premier Prince Sisowath Sirik Matak, who proclaim the establishment of the Khmer Republic. Sihanouk had tried to maintain Cambodian neutrality, but the communist Khmer Rouge, supported by their North Vietnamese allies, had waged a very effective war against Cambodian government forces. After ousting Sihanouk and taking control of the government, Lon Nol immediately set about to defeat the communists. Between 1970 and 1975, he and his army, the Forces Armees Nationale Khmer (FANK), with U.S. support and military aid, would battle the Khmer Rouge communists for control of Cambodia.
When the U.S. forces departed South Vietnam in 1973, both the Cambodians and South Vietnamese found themselves suddenly fighting the communists alone. Without U.S. support, Lon Nol's forces succumbed to the Khmer Rouge in April 1975. The victorious Khmer Rouge evacuated Phnom Penh and began reordering Cambodian society, which resulted in a killing spree and the notorious "killing fields." Eventually, hundreds of thousands of Cambodians were murdered or died from exhaustion, hunger, and disease. During the five years of bitter fighting for control of the country, approximately 10 percent of Cambodia's 7 million people died.