Cambodian Campaign (1970): The US Incursion Into Cambodia

The Cambodian Campaign was a military offensive by United States and South Vietnamese forces into eastern Cambodia between 29 April and 22 July 1970. Its aim was to destroy the bases and supply depots that North Vietnamese and Viet Cong troops used across the border. Militarily it captured huge quantities of supplies, but politically it was explosive: it widened the Vietnam War and provoked some of the largest protests in American history.

Background: Cambodia’s sanctuaries

Cambodia, under Prince Norodom Sihanouk, tried to stay neutral in the Vietnam War. In practice, North Vietnamese and Viet Cong forces used the thinly populated border areas as rear bases, hospitals and depots, supplied both by the Ho Chi Minh Trail and through the Cambodian port of Sihanoukville. In March 1969 the United States began secret B-52 bombing of these areas, known as Operation Menu.

On 18 March 1970, while Sihanouk was abroad, the Cambodian National Assembly removed him from power. The new government, led by General Lon Nol, demanded that Vietnamese communist forces leave. Instead, North Vietnamese troops attacked Cambodian forces and moved westward, threatening Phnom Penh. Sihanouk, in exile in Beijing, allied himself with the Cambodian communists, the Khmer Rouge.

The decision

President Richard Nixon, who was withdrawing American troops under the policy of Vietnamization, argued that the sanctuaries threatened both the remaining US forces and the South Vietnamese army. On 30 April 1970 he announced the operation in a televised address, presenting it as a limited action to protect American lives rather than an invasion of Cambodia. He also named as a target the Central Office for South Vietnam (COSVN), the communist command for the South.

The offensive

South Vietnamese forces crossed into the “Parrot’s Beak”, a part of Cambodia that juts towards Saigon, on 29 April. On 1 May US and South Vietnamese units, including the 1st Cavalry Division and the 11th Armored Cavalry Regiment, attacked the “Fishhook” area further north. Other operations followed along the border. American forces were limited to a zone about 30 kilometres deep inside Cambodia.

Most communist units withdrew westward rather than fight. COSVN, a mobile network rather than a single headquarters, was never found. But the allies discovered vast stores, including one complex in the Fishhook area that soldiers nicknamed “The City”. US figures list more than 20,000 individual weapons, about 2,500 crew-served weapons and several thousand tonnes of rice captured, along with large amounts of ammunition.

US ground forces left Cambodia by 30 June 1970, the deadline Nixon had set. South Vietnamese operations continued until 22 July. According to US figures, about 340 Americans and around 800 South Vietnamese soldiers were killed; the US claimed more than 10,000 communist soldiers killed, a figure that is difficult to verify.

A military success?

Supporters of the operation, including many US commanders, pointed to the quantity of supplies destroyed or captured and to the fall in communist activity in the provinces around Saigon over the following year. Critics replied that the North Vietnamese quickly rebuilt their supply system further west and that the main enemy units escaped. Historians generally agree that the campaign gave short-term relief to South Vietnam but did not change the course of the war.

Protests at home

The announcement shocked many Americans who believed the war was winding down. Hundreds of college campuses saw strikes and demonstrations. On 4 May 1970, at the Kent State shootings in Ohio, National Guardsmen fired on students, killing four and wounding nine. On 15 May police killed two students at Jackson State College in Mississippi. Around 100,000 protesters gathered in Washington on 9 May.

Congress also reacted. In June 1970 the Senate passed the Cooper–Church Amendment to cut off funds for US ground forces in Cambodia, and voted to repeal the Gulf of Tonkin Resolution of 1964, which had authorised the war’s escalation. A modified version of the Cooper–Church restrictions was passed by Congress in December 1970 and signed into law in January 1971.

Consequences in Cambodia

The campaign delayed major North Vietnamese offensives in the southern part of South Vietnam, and supporters argue it bought time for Vietnamization. In Cambodia, however, communist forces moved deeper inland and the country was pulled fully into the war. The civil war between Lon Nol’s government and the Khmer Rouge intensified, accompanied by heavy US bombing, until the Khmer Rouge took Phnom Penh in April 1975 and began the regime responsible for the Cambodian genocide.

Timeline

• 1969, 18 March: Secret US bombing of Cambodian border areas (Operation Menu) begins.
• 1970, 18 March: Prince Sihanouk is removed from power; Lon Nol leads the new government.
• 1970, 29 April: South Vietnamese forces enter the Parrot’s Beak.
• 1970, 30 April: Nixon announces the incursion on national television.
• 1970, 1 May: US and South Vietnamese forces attack the Fishhook.
• 1970, 4 May: Four students are killed at Kent State University.
• 1970, 30 June: The last US ground troops leave Cambodia.
• 1970, 22 July: South Vietnamese operations in the border areas end.

Why it matters

The Cambodian Campaign showed how a limited military operation could have unlimited political effects. It deepened divisions in the United States, strengthened Congress’s efforts to restrain the president’s war powers, and helped draw Cambodia into the catastrophe that followed.