The Khmer kingdoms of Cambodia flourish from the ninth to thirteenth centuries, reaching their apogee at the end of the 12th Century, after which they undergo a gradual decline.

From the 15th Century Cambodia is eclipsed by the neighbouring 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 but the interests of the colonialists soon take precedence.

When the Japanese dissolve the French administration in March 1945 the country achieves a short-lived but compromised independence lasting until the French return in October following the end of the Second World War.

Complete independence is finally granted in November 1953, with Prince Norodom Sihanouk establishing a 16-year rule based on an eclectic mix of populism, Khmer nationalism and state socialism.

The region is soon destabilised by the war in Vietnam. Sihanouk establishes ties with North Vietnam, the Viet Cong 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 begins to mount. A ruthless clampdown on opponents forces many to go underground and take up arms, including the Khmer Rouge, the radical wing of the Kampuchean Communist Party (KCP) led by Saloth Sar, later to be known across the world as Pol Pot.

The threat of the communist insurgents, the effects of the lack of US aid, an increase in incursions by the North Vietnamese and Viet Cong and the subsequent counterstrikes by US and South Vietnamese forces lead Sihanouk to reevaluate the country's relations with Washington. But by the time he turns back to the US in June 1969 it is too late.

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