Nuon Chea
In March 1970, Prince Sihanouk was deposed by his pro-American prime minister Lon Nol, who demanded that North Vietnamese troops leave Cambodia or face military action. Lon Nol began rounding up Vietnamese civilians in Cambodia into internment camps and massacring them, provoking harsh reactions from both the North Vietnamese and South Vietnamese government. North Vietnam invaded Cambodia at the request of the Khmer Rouge following negotiations with deputy leader Nuon Chea. In April–May 1970, many North Vietnamese forces entered Cambodia in response to the call for help addressed to Vietnam by Nuon Chea. Nguyen Co Thach recalls: "Nuon Chea has asked for help and we have liberated five provinces of Cambodia in ten days." U.S. and ARVN forces launched the Cambodian Campaign to attack PAVN and Viet Cong bases. A counter-offensive later that year as part of Operation Chenla II by the PAVN would recapture most of the border areas and decimate most of Lon Nol's forces.