As a result of the Geneva Conference on Indochina, Cambodia was able to bring about the withdrawal of the Viet Minh troops from its territory and to withstand any residual impingement upon its sovereignty by external powers.

Neutrality was the central element of Cambodian foreign policy during the 1950s and 1960s. By the mid-1960s, parts of Cambodia’s eastern provinces were serving as bases for North Vietnamese Army and Viet Cong (NVA/VC) forces operating against South Vietnam, and the port of Sihanoukville was being used to supply them. As NVA/VC activity grew, the United States and South Vietnam became concerned, and in 1969, the United States began a fourteen month long series of bombing raids targeted at NVA/VC elements, contributing to destabilization. Prince Sihanouk, fearing that the conflict between communist North Vietnam and South Vietnam might spill over to Cambodia, steadfastly opposed the bombing campaign by the United States along the Vietnam-Cambodia border and inside Cambodian territory. Prince Sihanouk wanted Cambodia to stay out of the North Vietnam-South Vietnam conflict and was very critical of the United States government and its allies (the South Vietnamese government). The United States claims that the bombing campaign took place no further than ten, and later twenty miles (32 km) inside the Cambodian border, areas where the Cambodian population had been evicted by the NVA. Prince Sihanouk, facing internal struggles of his own, due to the rise of the Khmer Rouge, did not want Cambodia to be involved in the conflict. Sihanouk wanted the United States and its allies (South Vietnam) to keep the war away from the Cambodian border. Not only did Sihanouk try to keep the communist North Vietnamese soldiers from entering Cambodia territory, but he also did not allow the United States to use Cambodian air space and airports for military purposes. This upset the United States greatly. The United States saw Prince Sihanouk as a North Vietnamese sympathizer and a thorn on the United States, and using the CIA, it began plans to get rid of Sihanouk.

Throughout the 1960s, domestic Cambodian politics became polarized. Opposition to the government grew within the middle class and leftists including Paris-educated leaders like Son Sen, Ieng Sary, and Saloth Sar (later known as Pol Pot), who led an insurgency under the clandestine Communist Party of Kampuchea (CPK). Sihanouk called these insurgents the Khmer Rouge, literally the “Red Khmer.” But the 1966 national assembly elections showed a significant swing to the right, and General Lon Nol formed a new government, which lasted until 1967. During 1968 and 1969, the insurgency worsened. In August 1969, Lon Nol formed a new government. Prince Sihanouk went abroad for medical reasons in January 1970.