Modern-day Laos has its roots in the ancient Lao kingdom of Lan Xang, established in the 14th Century under King FA NGUM. For three hundred years Lan Xang included large parts of present-day Cambodia and Thailand, as well as all of what is now Laos. After centuries of gradual decline, Laos came under the control of Siam (Thailand) from the late 18th century until the late 19th century when it became part of French Indochina. The Franco-Siamese Treaty of 1907 defined the current Lao border with Thailand. In 1975, the Communist Pathet Lao took control of the government ending a six-century-old monarchy and instituting a strict socialist regime closly aligned to Vietnam. A gradual return to private enterprise and the liberalization of foreign investment laws began in 1986. Laos became a member of ASEAN in 1997.