The Lao people, the predominant ethnic group in present-day Laos, are a branch of the Tai peoples who by the 8th century CE had established a powerful kingdom, Nanzhao, in south-western China. These Tai people soon had to leave their land, due to repeated Mongol invasions by Kublai Khan. The first Laotian state, Lan Xang followed the Tai Kingdom under the ruler Fa Ngum. Under him Theravada Buddhism spread in the kingdom. He was succeeded by his son, upon whose death the land was invaded by the Vietnamese. Soon after the land was engaged in multiple wars with the kingdoms of Myanmar (Burma) and Siamese (Thai), which lasted for two centuries.

During the 18th century the three Laotian states, which were continually at loggerheads, tried to maintain their independence from the Myanmar and Siamese kingdoms, both of which were contending for control of the western segment of continental Southeast Asia. Disunity weakened the Laotian kingdoms and inevitably caused them to fall prey to the Siamese. The invasion began with Vien Chan becoming subject to the Siamese. Siamese expansion toward the northeast—where the mountain states were placed under the co-suzerainty of Vietnam and Luang Prabang—provoked the protests of the French, who had established a protectorate over Vietnam. France entered into negotiations with Bangkok (1886) to define the Siamese-Vietnamese frontier. The French organized this territory as a protectorate with its administrative centre at Vientiane, and allowed it autonomy in local matters. When the French were paying little attention to Laos, the Japanese invaded. In March 1945 the Japanese took over major portions of French Indochina, and the next month Laos was declared independent.

The Geneva Conference declared that Laos should be ruled by the royal government, and not undergo partition. Following of easy peace in hostilities broke out in 1959 and thus another conference in Geneva in May 1961 culminated in an agreement in July 1962 that called for the country to become neutral and for a tripartite government to be formed. This didn’t lead to any form of restoration of peace and the country had to suffer due to the Vietnamese war. When Vietnamese communists marched into Saigon and Phnom Penh, Laos also suffered a bloodless takeover by the communists in mid-1975. That ended the monarchy and established Lao People’s Democratic Republic.

To know more about the history of Laos, refer to the following link:
https://www.britannica.com/place/Laos/History