The 1970 coup d'état that toppled Sihanouk dragged Cambodia into the vortex of a wider war. The escalating conflict pitted government troops, now renamed the Khmer National Armed Forces (Forces Armées Nationales Khmères--FANK--see Appendix B), initially against the North Vietnamese and the Viet Cong, and subsequently against the old RAK, now revitalized and renamed the Cambodian People's National Liberation Armed Forces (CPNLAF--see Appendix B).

As combat operations quickly disclosed, the two sides were mismatched. The inequality lay not so much in sheer numbers. Thousands of young urban Cambodians flocked to join FANK in the months following the coup and, throughout its five-year life, the republican government forces held a numerical edge over their opponents, the padded payrolls and the phantom units reported in the press notwithstanding. Instead, FANK was outclassed in training and leadership. With the surge of recruits, the government forces expanded beyond their capacity to absorb the new inductees. Later, given the press of tactical operations and the need to replace combat casualties, there was insufficient time to impart needed skills to individuals or to units, and lack of training remained the bane of FANK's existence until its collapse. While individual soldiers and some government units fought bravely, their leaders-- with notable exceptions--were both corrupt and incompetent. Arrayed against an armed force of such limited capability was arguably the best light infantry in the world at the time--the North Vietnamese and the Viet Cong. And when there forces were supplanted, it was by the tough, rigidly indoctrinated peasant army of the CPNLAF with its core of Khmer Rouge leaders.

With the fall of Sihanouk, the North Vietnamese and the Viet Cong became alarmed at the prospect of a pro-Western regime that might allow the United States to establish a military presence on their western flank. To prevent this from happening, they began transferring their military installations away from the border area to locations deeper within Cambodian territory. A new command center was established at the city of Kracheh (Kratié). On April 29, 1970, South Vietnamese and United States units unleashed a multi-pronged offensive into Cambodia to destroy the Central Office for South Vietnam (COSVN), the headquarters for North Vietnamese and Viet Cong combat operations in South Vietnam. Extensive logistical installations and large amounts of supplies were found and destroyed, but as reporting from the United States MACV subsequently disclosed, still larger amounts of material already had been moved deeper into Cambodia.

The North Vietnamese army turned on the republican government forces, and by June 1970, three months after the coup, they and the CPNLAF had swept FANK from the entire northeastern third of the country. After defeating the government forces, they turned newly won territories over to the local insurgents. The Khmer Rouge also established "liberated areas" in the south and the southwestern parts of the country, where they operated independently of the Vietnamese. The KCP's debt to the North Vietnamese after March 1970 was one that Pol Pot was loath to acknowledge; however, it is clear that without North Vietnamese and Viet Cong assistance, the revolutionary struggle would have dragged on much longer than it did.

United States bombing of enemy troop dispositions in Cambodia-- particularly in the summer of 1973, when intense aerial bombardment (known as Arclight) was used to halt a Khmer Rouge assault on Phnom Penh--bought time for the Lon Nol government, but did not stem the momentum of the communist forces. United States official documents give a figure of 79,959 sorties by B-52 and F-111 aircraft over the country, during which a total of 539,129 tons of ordnance were dropped, about 350 percent of the tonnage (153,000 tons) dropped on Japan during World War II. Many of the bombs that fell in Cambodia struck relatively uninhabited mountain or forest regions; however, as declassified United States Air Force maps show, others fell over some of the most densely inhabited areas of the country, such as Siemreab Province, Kampong Chhnang Province, and the countryside around Phnom Penh. Deaths from the bombing are extremely difficult to estimate, and figures range from a low of 30,000 to a high of 500,000. Whatever the real extent of the casualties, the Arclight missions over Cambodia, which were halted in August 15, 1973, by the United States Congress, delivered shattering blows to the structure of life in many of the country's villages, and, according to some critics, drove the Cambodian people into the arms of the Khmer Rouge.

The bombing was by far the most controversial aspect of the United States presence in Cambodia. In his book Sideshow, William Shawcross provides a vivid image of the hellish conditions, especially in the months of January to August 1973, when the Arclight sorties were most intense. He claims that the bombing contributed to the forging of a brutal and singlemindedly fanatical Khmer Rouge movement. However, his arguments have been disputed by several United States officials--including the former ambassador to Cambodia, Emory C. Swank, and the former Air Force commander in Thailand, General John W. Vogt--in an appendix to the second volume of the memoirs of then Secretary of State, Henry Kissinger.

From the Khmer Rouge perspective, however, the severity of the bombings was matched by the treachery of the North Vietnamese. The Cambodian communists had refused to take part in the Paris peace talks. When North Vietnam and the United States signed the Paris Peace Accords on January 27, 1973, bombing missions over Vietnam and Laos were terminated. The fighter bombers and other aircraft thus released were diverted to strike Khmer Rouge positions in Cambodia.

Data as of December 1987