In a post Second World War order in which nations belonged to either the camp led by the United States or by the Soviet Union, Cambodia was a nonaligned country. At the 1954 Geneva Conference, it had been agreed that all foreign forces would withdraw from Cambodia, that it would refrain from joining any military alliance, and that no foreign bases would be established on its sovereign territory.

Prince Norodom Sihanouk's Great Balancing Act

In relations with more powerful forces affecting his nation and with competing factions in his own country, Cambodian Head of State Prince Norodom Sihanouk was a master of the balancing act and a survivor. Alarmed by growing anarchy in South Vietnam, Cambodia severed diplomatic ties with Saigon in August 1963. Diplomatic relations with the United States were severed in May 1965. A 1965 deal with China and North Vietnam allowed the North Vietnamese Army to build permanent military facilities on Cambodian territory, while opening the port of Kompong Som ("Sihanoukville") to military supply shipments from China and the Soviet Union. Those supplies were destined for the North Vietnamese base camps in Eastern Cambodia.

In the late 1960s, Sihanouk moved to improve relations with the West. North Vietnam's use of Eastern Cambodia as a sanctuary for military units was putting Cambodian neutrality in jeopardy. The Cultural Revolution made China a difficult partner to deal with, politically and economically. South Vietnam had not collapsed, even in the face of the 1968 Tet Offensive. A loss of economic and military aid from the United States and the unavailability of American military equipment and spare parts had also inspired second thoughts in Phnom Penh regarding its break with Washington.

At the same time, newly inaugurated U.S. President Richard Nixon was seeking to withdraw from Southeast Asia under honorable conditions, avoiding defeat and projecting a strong image. Hitting North Vietnamese bases in Cambodia would buy time for South Vietnam to learn to defend its own borders, enhancing the likelihood of success for Nixon's Vietnamization policy.

The Central Office for South Vietnam

The Central Office for South Vietnam (COSVN) was organized in 1961 by the Central Committee of the Workers Party of Vietnam (the Communist Party) in Hanoi, to direct Viet Cong political and military operations in South Vietnam. People's Army of Vietnam General Nguyễn Chí Thanh, a member of the Workers Party of Vietnam political bureau, arrived in late 1963 or early 1964 to serve as COSVN's leading strategist and military commander. He continued in that role through late 1967, when he returned to Hanoi to deliver his plan for the Tet Offensive and died of a heart attack while there.

On the ground, the organization was composed of individuals living in thatched huts in jungle surroundings, constantly on the move in order to avoid U.S. bombing raids and search and destroy operations. During the early 1960s, COSVN was located northwest of Saigon, near South Vietnam's border with Cambodia. Later in the 1960s, the headquarters was in and around Cambodia's "Fishhook" region, a salient protruding into Vietnamese territory approximately 80 kilometers northwest of Saigon.

Why Nixon Decided to Bomb Cambodia

On February 22, North Vietnam launched its Tet 1969 offensive, in accordance with COSVN Directive Number 71, which had been issued on January 31, 1969. This offensive consisted of a coordinated series of sapper attacks, artillery and rocket bombardments targeting U.S. military forces and installations, including critical command and control nodes, primarily around Saigon and Da Nang.

These attacks were quickly repulsed, albeit at a steep cost: More than 1,140 Americans and 1,500 South Vietnamese were killed over three weeks of fighting. During the transition period preceding the 1969 Presidential inauguration, Nixon had made overtures to the North Vietnamese expressing a desire to work out of an honorable settlement. In White House Years, Henry Kissinger, who had just become the National Security Advisor, described North Vietnam's offensive as an act of extraordinary cynicism , given the new American administration's interest in finding a way out of the conflict. He adds that Nixon was seething , and that All [Nixon's] instincts were to respond violently to Hanoi's cynical maneuver .

The scales had been tipped in favor of suggestions recently made by top defense officials urging President Nixon to bomb North Vietnamese sanctuaries in eastern Cambodia. Chairman of the Joint Chiefs of Staff Earle Wheeler had made this suggestion on January 30, only ten days after the 1969 inauguration. On February 9, Military Assistance Command in Vietnam (MACV) commander General Creighton Abrams had requested approval for B-52 raids on the North Vietnamese sanctuaries, based on intelligence sources including the testimony of a Viet Cong defector, photographs from reconnaissance overflights and MACV analysis.

Operation Menu

In a February 25 memorandum, Secretary of Defense Melvin Laird advised I believe it would be better to hold this attack for a period in which the scope, intensity, and duration of enemy-initiated activity are at more pronounced levels. In his memoirs, Kissinger observed I thought that a failure to react to so cynical a move by Hanoi could doom our hopes for negotiations; it could only be read by Hanoi as a sign of Nixon’s helplessness in the face of domestic pressures; .

On March 15, the North Vietnamese fired five rockets into Saigon. Kissinger received a phone call from Nixon on that very day, in which he was informed that the President was ordering an immediate B‐52 attack on the Cambodian sanctuaries. This developed into Operation Menu, a covert series of six B-52 "carpet bombing" missions against targets in eastern Cambodia that ended on May 26, 1970. The first mission consisted of a humongous raid by 60 B-52 Stratofortress strategic bombers flying out of Andersen Air Force Base in Guam, targeting COSVN in the Fishhook region. COSVN was not destroyed in the raid.