Cambodian coup of 1970

The Cambodian coup of 1970 (Khmer: រដ្ឋប្រហារឆ្នាំ ១៩៧០) refers to the removal of the Cambodian Head of State, Prince Norodom Sihanouk, after a vote in the National Assembly on 18 March 1970. Emergency powers were subsequently invoked by the Prime Minister Lon Nol, who became effective head of state, and led ultimately to the proclamation of the Khmer Republic later that year. It is generally seen as a turning point in the Cambodian Civil War. No longer a monarchy, Cambodia was semi-officially called "État du Cambodge" (State of Cambodia) in the intervening six months after the coup, until the republic was proclaimed.

It also marked the point at which Cambodia became substantially involved in the Vietnam War, as Lon Nol issued an ultimatum to North Vietnamese forces to leave Cambodia.

Since independence from France in 1954, Cambodia had been led by Prince Norodom Sihanouk, whose Sangkum political movement had retained power after winning the 1955 parliamentary election. In 1963, Sihanouk had forced the National Assembly to approve a constitutional amendment that made him head of state with no fixed term of office. He had retained domestic power through a combination of political manipulation, intimidation, patronage, and careful balancing of left- and right-wing elements within his government; whilst placating the right with nationalist rhetoric, he appropriated much of the language of socialism to marginalize the Cambodian communist movement, whom he called the Khmers rouges ("Red Khmers").

With the Second Indochina War escalating, Sihanouk's balancing act between left and right became harder to maintain. Cross-border smuggling of rice also began to have a serious effect on the Cambodian economy. In the Cambodian elections of 1966, the usual Sangkum policy of having one candidate in each electoral district was abandoned; there was a huge swing to the right, especially as left-wing deputies had to compete directly with members of the traditional elite, who were able to use their local influence. Although a few communists within the Sangkum – such as Hou Yuon and Khieu Samphan – chose to stand, most leftists were decisively defeated. Lon Nol, a rightist who had been a longstanding associate of Sihanouk, became Prime Minister.

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