The official History of Laos as introduced in government textbooks, is conventionally traced to the establishment of the kingdom of Lan Xang by Fa Ngum in 1353. This is a relatively conservative date to begin the history of the nation, providing a contrast to the course taken by Thai historiography (which reaches back implausibly far into proto-history). By the 14th century, when this "official history" begins, the speakers of early Lao-related languages had probably developed a reasonable base of population among the prior inhabitants of (what is now) Laos over the prior century or two.
The Lao state dates only from 1945. The idea of a separate Lao nationality was formed during the 19th century, when western ideas of national identity reached South-East Asia, and when the Lao-speaking peoples were being squeezed between two expansionist powers, Siam (Thailand) and Annam (Vietnam). The current borders of Laos were created by France in 1893 and 1904. But in reality the Lao share a common history with the Siamese and other people of the Tai language group, and Lān Xāng was only one of a number of Tai kingdoms in a region which had a broad linguistic and cultural unity before the arrival of outside powers.