The Khmer kingdoms of Cambodia flourish from the 9th to 13th centuries, reaching a high point at the end of the 12th Century, after which they undergo a gradual decline.
From the 15th Century onwards Cambodia is squeezed by the neighbouring kingdoms in Thailand and Vietnam, with both progressively encroaching on Cambodian territory. Attempts by the Vietnamese to impose their culture on the Cambodians set the seeds for an abiding distrust. The encroachment is halted in 1863 when Cambodia agrees to become a French protectorate.
Cambodia achieves a short-lived but compromised independence when the Japanese dissolve the French administration in March 1945. French control is reimposed following the end of the Second World War.
Complete independence is finally granted in November 1953. Prince Norodom Sihanouk becomes head of state and head of the government. His 16-year rule uses an eclectic mix of authoritarianism, populism, Khmer nationalism and state socialism to navigate the growing internal and external pressures building on Cambodia.
Principal among these pressures is the destabilised of the region caused by the war in Vietnam. Sihanouk establishes ties with North Vietnam, the Viet Cong (South Vietnamese communists) and China and distances the country from the United States, which he believes is plotting against him. In November 1963 he terminates the US aid program and in May 1965, as the war spills into Cambodia, breaks relations completely.
Meanwhile, domestic opposition to Sihanouk starts to mount. Disaffected groups begin to go underground and take up arms. Included among the groups is the Khmer Rouge, the radical wing of the Kampuchean Communist Party. The Khmer Rouge is led by Saloth Sar, later to be known to the world as Pol Pot.