The Laotians are descendants of Thai tribes that were pushed southward from Yunnan, China, in the 13th cent. and gradually infiltrated the territory of the Khmer Empire. In the mid-14th cent. a powerful kingdom called Lan Xang was founded in Laos by Fa Ngoun (1353–73), who is also credited with the introduction of Theravada Buddhism and much of Khmer civilization into Laos. Lan Xang waged intermittent wars with the Khmer, Burmese, Vietnamese, and Thai, and by the 17th cent. it held sway over sections of Yunnan, China, of S Myanmar, of the Vietnamese and Cambodian plateaus, and large stretches of N Thailand. In 1707, however, internal dissensions brought about a split of Lan Xang into two kingdoms: Luang Phabang in upper (northern) Laos and Vientiane in lower (southern) Laos. During the next century the two states, constantly quarreling, were overrun by the armies of neighboring countries.
In the early 19th cent. Siam was dominant over the two Laotian kingdoms, although Siamese claims were disputed by Annam. After French explorations in the late 19th cent. Siam was forced (1893) to recognize a French protectorate over Laos, which was incorporated into the union of Indochina. During World War II, Laos was gradually occupied by the Japanese, who in 1945 persuaded the king of Luang Phabang to declare the country's independence.
In 1946 the French reestablished dominion over Laos, recognizing the king as constitutional monarch of the entire country. The French granted an increasing measure of self-government, and in 1949 Laos became a semiautonomous state within the French Union. In 1951, a Communist Laotian nationalist movement, the Pathet Lao, was formed by Prince Souphanouvong in North Vietnam. In 1953, Pathet Lao guerrillas accompanied a Viet Minh invasion of Laos from Vietnam and established a government at Samneua in N Laos. That year Laos attained full sovereignty; admission into the United Nations came in 1955.
The new country faced immediate civil war as Pathet Lao forces, supported by the Viet Minh, made incursions into central Laos, soon occupying sizable portions of the country. Agreements reached at the Geneva Conference of 1954 provided for the withdrawal of foreign troops and the establishment of the Pathet Lao in two northern provinces. In 1957 an agreement was reached between the royal forces and the Pathet Lao, but in 1959 the coalition government collapsed and hostilities were renewed.
A succession of coups resulted (1960) in a three-way struggle for power among neutralist, rightist, and Communist forces. The Communist Pathet Lao rebels remained under the leadership of Prince Souphanouvong in the northern provinces. The right-wing government of Boun Oum, installed in Vientiane, was recognized by the United States and other Western countries and controlled the bulk of the royal Laotian army. The Soviet Union and its allies continued to recognize the deposed neutralist government of Souvanna Phouma, who had fled to neighboring Cambodia.
In May, 1961, with Pathet Lao and neutralist forces in control of about half the country, a cease-fire was arranged. A 14-nation conference convened in Geneva, producing (1962) another agreement providing for the neutrality of Laos under a unified government. A provisional coalition government, with all factions represented, was accordingly established under the premiership of Souvanna Phouma. Attempts to integrate the three military forces failed, however, and the Pathet Lao began moving against neutralist troops.
Open warfare resumed in 1963, and the Pathet Lao, bolstered by supplies and troops from North Vietnam, solidified control over most of N and E Laos. Disgruntled right-wing military leaders staged a coup in 1964 and attempted to force the resignation of Souvanna Phouma; the United States and the Soviet Union emphasized their support of the premier, however, and he remained in office with a right-wing neutralist government.
Pathet Lao guerrilla activity decreased after the start (1965) of U.S. bombings of North Vietnamese military bases and communications routes. The bombings also included attacks on what came to be known as the Ho Chi Minh Trail, a North Vietnamese supply route through E Laos. Communist pressure increased during 1969, and early in 1970 the Pathet Lao launched several major offensives. Early in 1971, South Vietnamese troops invaded Laotian territory in an unsuccessful attempt to cut the Ho Chi Minh trail. The attack drove the North Vietnamese deeper into Laos, and Laos became another battleground of the Vietnam War, with heavy U.S. aerial bombardments.
During this period, the United States extended enormous military and economic aid to the Laotian government, armed Hmong tribes (who also fought in Vietnam), and financed the use of Thai mercenary troops, whose numbers peaked to over 21,000 in 1972. The Pathet Lao, supported by North Vietnamese troops, scored major gains, consolidating their control over more than two thirds of Laotian territory (but over only one third of the population). Heavy fighting persisted until Feb., 1973, when a cease-fire was finally declared. A final agreement between the government and the Pathet Lao, concluded in Sept., 1973, provided for the formation of a coalition government under the premiership of Souvanna Phouma (inaugurated in Apr., 1974), the stationing of an equal number of government and Pathet Lao troops in the two capitals, and the withdrawal of all foreign troops and advisers.
After Communist victories in Vietnam and Cambodia, the Pathet Lao took control of the country in 1975, abolished the monarchy, and made Laos a republic. Souphanouvong became president, and Kaysone Phomvihane, head of the Communist party, became premier. Huge numbers of Laotians (many Hmong) fled to Thailand and many eventually sought refuge in the United States. (Small Hmong forces, however, continued to fight against the Communists into the 21st cent.) Laos became increasingly dependent on Vietnam for military and economic assistance, and the two countries signed a 25-year treaty of friendship in 1977.
In the early 1990s Laos abandoned economic communism for capitalism, but the party retained tight political control, and political dissent was harshly suppressed. Meanwhile, the nation pursued improved relations with such former enemies as China, Thailand, and the United States. Kaysone became president in 1991. He died the following year and was succeeded as president by Nouhak Phoumsavan. Khamtay Siphandone, a former military leader of the Pathet Lao, became party leader and, when Nouhak retired in 1998, assumed the job of president as well. Laos was admitted to the Association of Southeast Asian Nations (ASEAN) in 1997. Khamtay retired as party leader in Mar., 2006; he was succeeded in the post by Vice President (and Lt. Gen.) Choummaly Sayasone, who also succeeded Khamtay as president in June, 2006.