armed forces of North Vietnam. As they gained control of Cambodian territory, the Vietnamese communists imposed a new political infrastructure, which was eventually dominated by the Cambodian communists now referred to as the Khmer Rouge. Between 1969 and 1973, Republic of Vietnam and US forces bombed Cambodia in an effort to disrupt the Viet Cong and Khmer Rouge. Documents uncovered from the Soviet archives after 1991 reveal that the North Vietnamese attempt to overrun Cambodia in 1970 was launched at the explicit request of the Khmer Rouge and negotiated by Pol Pot's then second in command, Nuon Chea. NVA units overran many Cambodian army positions while the Communist Party of Kampuchea (CPK) expanded their small-scale attacks on lines of communication. In response to the North Vietnamese invasion, US President Richard Nixon announced that US and South Vietnamese ground forces had entered Cambodia in a campaign aimed at destroying NVA base areas in Cambodia (see Cambodian Incursion). Although a considerable quantity of equipment was seized or destroyed by US and South Vietnamese forces, containment of North Vietnamese forces proved elusive. The Khmer Republic's leadership was plagued by disunity among its three principal figures: Lon Nol, Sihanouk's cousin Sirik Matak, and National Assembly leader In Tam. Lon Nol remained in power in part because neither of the others was prepared to take his place. In 1972, a constitution was adopted, a parliament elected, and Lon Nol became president. But disunity, the problems of transforming a 30,000-man army into a national combat force of more than 200,000 men, and spreading corruption weakened the civilian administration and army. The Communist insurgency inside Cambodia continued to grow, aided by supplies and military support from North Vietnam. Pol Pot and Ieng Sary asserted their dominance over the Vietnamese-trained communists, many of whom were purged. At the same time, the CPK forces became stronger and more independent of their Vietnamese patrons. By 1973, the CPK were fighting battles against government forces with little or no North Vietnamese troop support, and they controlled nearly 60% of Cambodia's territory and 25% of its population. The government made three unsuccessful attempts to enter into negotiations with the insurgents, but by 1974, the CPK were operating openly as divisions, and some of the NVA combat forces had moved into South Vietnam. Lon Nol's control was reduced to small enclaves around the cities and main transportation routes. More than 2 million refugees