Lan Xang
When the Lao kingdom of Lan Xang (Lan Chang) was established in Luang Prabang in the 14th century by Fa Ngum, with help from the Khmers. The kingdom's name means Million Elephants, echoing the name of the neighboring northern kingdom of Lanna, Million Fields. Lan Xang was to provide Isan with much of its later population. As the Khmer empire continued to retreat under pressure from the Thai kingdom of Ayutthaya, Lan Xang was able to expand its influence in Isan. Lao settlers might gradually moved across the Mekong into northern Isan between the 14th and 16th centuries. However no clear evidence suggests any significant settlement in hinterland Isan during this period. Ayutthaya which arose as a major power from the late 14th century, limited its border only at Nakhon Ratchasima and Phimai.
Read more about this topic: History Of Isan