 In official Thai documents the term "hill tribe" ("chao khao") began to appear in the 1960s.This term highlights a "hill and valley" dichotomy that is based on an ancient social relationship existing in most of northern and western Thailand, as well as in Sipsongpanna and northern Vietnam.For the most part the Dai/Tai/Thai occupied the more fertile intermontane basins and valleys, while the less powerful groups lived at the less rich higher elevations.