Lasting from 1953 to 1975, the Laotian Civil War was fought between the Communist Pathet Lao and the Royal Lao Government. Before 1953, Laos was part of Indochina and nominally under the control of the French Empire. But the reality was the French never got full control back after Indochina was conquered by the Japanese during World War II. So World War II ends, and the French sponsor a guerrilla war to retake control, while the nominal king proclaimed an end to French protectorate status while quietly supporting the French return, and a national liberation movement starts to take shape around some other Laotian princes, supported to a degree by the high percentage of Vietnamese living in urban Laos.
Eventually, the French gave up, leaving the country in 1953 and officially giving power to the Royal Lao government. The civil war got started immediately. It was treated as a proxy war by the great powers, with North Vietnam, Russia, and China supporting the Pathet Lao, and South Vietnam and the United States supporting the Royal Lao Government. At the time, however, the Laotian Civil War was largely ignored in favor of the Vietnam War which was happening at the same time. In the end the communists won, and their party continues to control the country.
Today, the Laotian Civil War is usually known by the nickname it was given in the 1960s by the CIA – “The Secret War.”