Judging from the description of the Nan-Chao kingdom as chronicled by the Chinese, We can say that Nan-Chao kingdom was a comparatively powerful state with a high level of culture. It lasted for some seven centuries until it fell in 1253 A.D. to Kublai Khan. the great Mogul emperor of China. The Nan-Chao kingdom during the zenith of her power, sometime in the 9th century A.D. might have extended her suzerainty southward to the sparsely populated territories in the North of Indo-China as hinted vaguely in the many earliest recorded histories and legends of the Thai, the Laos and the Shans. Hall in his "A history of South -East Asia" says that the Tai (or Thai) never ceased to be on the move. (from the earlier days of Nan-Chao) , and slowly that infiltrated along the rivers and down the valleys of Central Indo-China. Small groups settled among the Khmers, the Mons and the Burmese, and, long before that, they had been crossing into the Menam valley (in central Thailand) from the river Mekong and undoubtedly from the river Salween too.
Confining ourselves to the history of the Thai of Thailand, some tribes of the Thai migrated at different times and from different directions into present Thailand a thousand or more years ago. These are conjectural statements, compounded from inadequate evidence. At first they settled themselves in what is now the Northern Area of Thailand in many small independent states ruled by their own chief or kings. Not until the latter part of the 13th century A.D. Did the Northern Area of Thailand, with Chiang Mai as its capital, became a relatively fair-sized kingdom under its first king Mengrai.