April-June, 1970: Cambodia Invasion Summary

  • Last updated on November 11, 2022

In 1968, when Richard M. Nixon was voted into office, partly on the strength of his promise to bring peace to Vietnam, Cambodia was at peace. Its ruler, Prince Norodom Sihanouk, had successfully maneuvered to keep his country separate from the Vietnam War by allowing the North Vietnamese to use border provinces both as sanctuaries and to channel supplies destined for South Vietnam through Cambodian territory. For Sihanouk, the decision to aid the Vietnamese communists in this manner was one of expediency rather than sympathy. In his eyes, the choices were few; he must either help the communists or accept “American imperialism.”

In 1968, when Richard M. Nixon was voted into office, partly on the strength of his promise to bring peace to Vietnam, Cambodia was at peace. Its ruler, Prince Norodom Sihanouk, had successfully maneuvered to keep his country separate from the Vietnam War by allowing the North Vietnamese to use border provinces both as sanctuaries and to channel supplies destined for South Vietnam through Cambodian territory. For Sihanouk, the decision to aid the Vietnamese communists in this manner was one of expediency rather than sympathy. In his eyes, the choices were few; he must either help the communists or accept “American imperialism.”

According to the Nixon doctrine, in the future the United States would provide material support to troops of countries resisting communist aggression but refrain from sending U.S. personnel to the battlefield. The key to Nixon’s plan for ending the war was “Vietnamization,” a program calling for the gradual extrication of U.S. troops and their replacement by Vietnamese. In essence, it was a solution to the U.S. problem of disengaging from the war rather than a solution to the war. In the same way, the prospect of invading Cambodia was viewed only as a means to ease disengagement. That it would actually widen the war and introduce a previously neutral country to the conflict were possibilities that remained secondary considerations.

In April, 1964, U.S. planes, flying from bases in Thailand, strafed two Cambodian villages. Sihanouk soon severed diplomatic relations with the United States. Subsequent border forays by the South Vietnamese army into Cambodia, coordinated with U.S. military advisers, also had little effect on stopping the flow of support from North Vietnam to South Vietnam.

Background

The U.S. military leadership had, for some time, sought permission to invade Cambodia. President Nixon’s immediate predecessor, Lyndon B. Johnson, had rejected several requests on the grounds that the impact of such an invasion on the course of the war would be negligible. In February of 1969, however, less than a month after Nixon assumed office, General Creighton W. Abrams, commander of U.S. forces in Vietnam, requested that B-52 bombers be used against sanctuaries and supply routes. Nixon, in concurrence with his national security adviser, Henry A. Kissinger, agreed, and in March, 1969, the bombing of Cambodia began. As the U.S. Constitution specifically holds that only Congress can decide to wage war, this act to widen the war almost certainly was illegal. To prevent the issue of legality from arising, however, Nixon ordered that the bombing be kept secret. To prevent a news leak, he even bypassed the ordinary military chain of command, failing to notify the Pentagon. The domestic outcry over the bombing forced him to order a halt. In this manner, without the knowledge of Congress or the American people, Cambodia was introduced to the war one year prior to the U.S. invasion.

Although the bombing in itself achieved limited success in interdicting North Vietnamese supply routes and storage areas, it killed more Cambodians than North Vietnamese, had a significant impact on the Cambodian political situation, and was primarily responsible for initiating a series of events that would impact Cambodia’s future for years. First, it pushed the communists out of the border sanctuary areas and deeper into Cambodia. This irritated rightist elements in Sihanouk’s government who, already dissatisfied with his permissiveness in allowing Vietnamese communists access to Cambodian territory, became even more so as they witnessed the communists usurp still more. Sihanouk, aware of the discord, took measures to allay it. He reopened diplomatic relations with the United States. He informed Washington that he would not object to some attacks on Vietnamese sanctuaries inside Cambodia, but he never agreed to indiscriminate bombing. By not protesting the B-52 raids, which he strongly opposed, he felt he was making a significant concession to these same rightist elements who supported them. Fearing eventual annexation by Vietnam, rightist General Lon Nol, Cambodian armed forces commander, ordered all Vietnamese to leave the country, and anti-Vietnamese demonstrations were organized in Phnom Penh and the provinces along the Vietnamese border.

In March, 1970, as tensions continued to mount within his government, Sihanouk departed from Phnom Penh on a diplomatic mission to Moscow and Peking. Again, motivated by the need to settle the unrest among his ministers, he intended to urge both governments to restrain the North Vietnamese from encroaching further into Cambodian territory. However, he had failed to assess accurately how far the crisis in his capital had actually advanced. While still in Moscow, he learned he had been deposed by his pro-U.S. defense minister, Lon Nol. Although there is no evidence that the United States or any other foreign power promoted the coup, it precipitated crucial policy changes on both sides of the Vietnam War. The struggling Cambodian communist movement Khmer Rouge, which previously had been judged by Hanoi to be too small to be effective, was suddenly thrust by Sihanouk’s downfall into a position from which it could make a serious attempt at gaining power. As a result, Vietnamese assistance increased dramatically, and the Khmer Rouge received the support it needed eventually to achieve power. For those among the U.S. leadership who supported an invasion plan, Sihanouk’s downfall was a fortuitous event, since he alone among Cambodia’s leaders had remained strongly opposed. With his removal, all Cambodian government opposition to an invasion attempt ended.

The Invasion

On April 29–30, 1970, an invasion was mounted with thirty thousand U.S. and South Vietnamese troops crossing into Cambodia. Secrecy had so pervaded the operation’s planning that no one in Cambodia, including the United States mission and Lon Nol, learned of it until after it occurred. Although Nixon spoke of the invasion as a decisive victory, the military regarded it as having attained a temporary advantage at best. While uncovering enormous stores of supplies, it encountered few enemy troops. In effect, military planners had failed to take into account the communists’ move westward under the impact of the bombing. Thus, while temporarily disrupting the communists’ logistics, the invasion made little impact on their long-term conduct of the war. Pentagon estimates suggested that North Vietnamese plans for an offensive had been set back by no more than a year; in keeping with this assessment, the North Vietnamese, within two months of the withdrawal of United States invasion forces, had reestablished their supply trails and sanctuaries.

Within the United States, the effect of the invasion was devastating. The antiwar movement reacted with intensified demonstrations and student strikes. The deaths of four students at Kent State University as the result of a confrontation between National Guardsmen and protesters shocked the nation. The extent of the reaction engendered by the invasion surprised President Nixon. Although he defended his action to the American people, his arguments appeared flimsy and misrepresentative. Claiming that the United States had for five years respected Cambodian neutrality, he neglected to mention the bombing. Declaring that the invasion was intended to destroy the headquarters for the entire communist military operation in South Vietnam, he ignored overwhelming evidence offered by the military proving that no such target existed. Depicting the invasion as a necessary step taken against the North Vietnamese to preclude the possibility of attacks on U.S. troops withdrawing from the war, he hid the fact that during the course of negotiations for peace, the North Vietnamese had already offered to refrain from such attacks once a withdrawal date was determined. Finally, asserting that his decision was crucial to the maintenance of U.S. prestige abroad, Nixon contradicted evidence indicating a substantial fall in U.S. prestige following the invasion. Both internationally and domestically, the feeling prevailed that the president had succeeded only in expanding an already wearisome war.

Impact

For Cambodia, the invasion completed the destruction of a tenuous neutrality already severely damaged for more than a year by the bombing campaign. It precipitated an internal war that had not existed before U.S. forces crossed the border and that subsequently enveloped Cambodia in a prolonged conflict between United States-supported anti-communist forces and Vietnam-supported Khmer Rouge insurgents, thereby subjecting the country to still further devastation and eventual communist rule.

In this way, the fate of Cambodia was decided. U.S. policymakers, interested only in exploiting Cambodia’s territory as an adjunct to the Vietnam War, held the welfare of Cambodians and their land in small regard. President Nixon made this clear when in December, 1970, he stated that the Cambodians were “tying down forty thousand North Vietnamese regulars [in Cambodia and] if those North Vietnamese weren’t in Cambodia they’d be over killing Americans.” The Cambodians were thus reduced to acting as surrogate U.S. targets for North Vietnamese guns. The tragedy of the U.S. invasion was that so much was suffered for so little reason.

Cambodia was but a sideshow for Nixon, who failed to take either the subtleties of Indochina or the domestic antiwar movement into account. Sihanouk’s assessment of policymakers in Washington was, in characteristic hyperbole, that “They demoralized America, they lost all of Indochina to the communists, and they created the Khmer Rouge.”

When U.S. and Vietnamese troops withdrew from Cambodia, civil war ensued. The Khmer Rouge, which came to power in 1975, soon attacked Vietnam to regain lost territory. Hanoi counterattacked in 1978, pushing the Khmer Rouge to the border with Thailand by 1979. In 1989, Vietnamese troops withdrew, and in 1993, the United Nations held elections, resulting in an elected parliament, which restored Sihanouk as king of Cambodia.

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