In fact throughout its history, Laos were ruled by the various local empires such as the Khmers from Cambodia. It was around the 14th century that a small kingdom called Lun Xang was founded by the Laotians. By the 16th century, it was threatened by Burma but by the 18th century, Lun Xang split into three regions and Siam forces occupied Vientiane and the other regions.
By the late 19th century, French influnce in the region grew and in 1893, the Siamese surrendered all territory east of the River Mekong to the French including today's Laos.
During the Japanese occupation in the second world war, parts of Laos were given to Thailand. The king declared independence from France after the War but France invaded the country in 1946 and were in control up to about 1953. By then, Laos was divided, most of it ruled by the Royalist government and the other parts ruled by a political party, Paphet Lao.
In the 1960s, Laos was drawn into the Vietnam war. From 1964 to 1973, Laos was also bombed. When South Vietnam and Cambodia governments fell, the ruling government in Laos was also replaced by the Paphet Lao. Laos joined ASEAN in 1997.
I have only seen the airport and everything in between the airport and the hotel I am staying in. What I can see is a lot of modern infrastructure. The Wattay International Airport is modern and complete with aerobridges. The roads are nice and wide. There was not much traffic though. For a first impression, I must admit Vientiane was much more developed than what most people say.