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The Laotian Civil War was waged between the Communist Pathet Lao and the Royal Lao Government from 23 May 1959 to 2 December 1975. The Kingdom of Laos was a covert theater during the Vietnam War with both sides receiving heavy external support in a proxy war between the global Cold War superpowers. The fighting also involved the North Vietnamese, South Vietnamese, American and Thai armies, both directly and through irregular proxies. The war is known as the Secret War among the American CIA Special Activities Center, and Hmong and Mien veterans of the conflict. The Franco–Lao Treaty of Amity and Association transferred remaining French powers to the Royal Lao Government, establishing Laos as an independent member of the French Union. However, this government did not include representatives from the Lao Issara anti-colonial armed nationalist movement. The following years were marked by a rivalry between the neutralists under Prince Souvanna Phouma, the right wing under Prince Boun Oum of Champassak, and the left-wing Lao Patriotic Front under Prince Souphanouvong and half-Vietnamese future Prime Minister Kaysone Phomvihane. Several attempts were made to establish coalition governments, and a "tri-coalition" government was finally seated in Vientiane. The North Vietnamese Army, in collaboration with the Pathet Lao, invaded Laos in 1958 and 1959, occupying the east of the country to use for its Ho Chi Minh Trail supply corridor and as a staging area for offensives into South Vietnam. There were two major theatres of the war, one for control over the Laotian Panhandle and the other was fought around the northern Plain of Jars. From 1961 onward, the US trained Hmong tribesmen to disrupt North Vietnamese operations and in 1964, the US began bombing North Vietnamese supply routes. The North Vietnamese and Pathet Lao eventually emerged victorious in December 1975, following from North Vietnam's final victory over South Vietnam in April 1975. After the communist takeover in Laos, up to 300,000 people fled to neighbouring Thailand, and Hmong rebels began an insurgency against the new government. The Hmong were persecuted as traitors and "lackeys" of the Americans, with the government and its Vietnamese allies carrying out human rights abuses against Hmong civilians. The incipient conflict between Vietnam and China also played a role with Hmong rebels being accused of receiving support from China. Over 40,000 people died in the conflict. The Lao royal family were arrested by the Pathet Lao and sent to labor camps, where most of them died in the late 1970s and 1980s, including King Savang Vatthana, Queen Khamphoui and Crown Prince Vong Savang.