Menu. 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 governments. In April–May 1970, North Vietnam invaded Cambodia at the request of the Khmer Rouge following negotiations with deputy leader 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 in May to attack PAVN and Viet Cong bases. A counter-offensive in 1971 as part of Operation Chenla II by the PAVN would recapture most of the border areas and decimate most of Lon Nol's forces. The U.S. incursion into Cambodia sparked nationwide U.S. protests as Nixon had promised to deescalate the American involvement. Four students were killed by National Guardsmen in May 1970 during a protest at Kent State University in Ohio, which provoked further public outrage in the United States. The reaction to the incident by the Nixon administration was seen as callous and indifferent, reinvigorating the declining anti-war movement. The U.S. Air Force continued to heavily bomb Cambodia in support of the Cambodian government as part of Operation Freedom Deal. Laos Building up on the success of ARVN units in Cambodia, and further testing the Vietnamization program, the ARVN were tasked to launch Operation Lam Son 719 in February 1971, the first major ground operation aimed directly at attacking the Ho Chi Minh trail by attacking the major crossroad of Tchepone. This offensive would also be the first time the PAVN would field-test its combined arms force. The first few days were considered a success but the momentum had slowed after fierce resistance. Thiệu had halted the general advance, leaving armoured divisions able to surround them. Thieu had ordered air assault troops to capture Tchepone and withdraw, despite facing four-times larger numbers. During the withdrawal the PAVN counterattack had forced a panicked rout. Half of the ARVN troops involved were either captured or killed, half of the ARVN/US support helicopters were downed by anti-aircraft fire and the operation was considered a fiasco, demonstrating operational deficiencies still present within the ARVN. Nixon and Thieu had sought to use this event to show-case victory simply