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.