The Kingdom of Cambodia, also known as the First Kingdom of Cambodia, and commonly referred to as the Sangkum period, refers to Norodom Sihanouk's first administration of Cambodia from 1953 to 1970, an especially significant time in the country's history. Sihanouk continues to be one of the most controversial figures in Southeast Asia's turbulent and often tragic postwar history. From 1955 until 1970, Sihanouk's Sangkum was the sole legal party in Cambodia.^[84]

Following the end of World War II, France restored its colonial control over Indochina but faced local resistance against their rule, particularly from Communist guerilla forces. On 9 November 1953 it would achieve independence from France under Norodom Sihanouk but still faced resistance from Communist groups such as United Issarak Front. As the Vietnam War escalated, Cambodia sought to remain its neutrality but in 1965, North Vietnamese soldiers were allowed to set bases up and in 1969, the United States began a bombing campaign against North Vietnamese soldiers in Cambodia. The Cambodian monarchy would be abolished in a US-backed coup on October 9, 1970 headed by Prime Minister Lon Nol who established the Khmer Republic which lasted until the fall of Phnom Penh in 1975.^[85]