The ancestors of present-day Malays, Dais, Bais, Khymers, Mons, Burmans Viets, Hmongs, Kadais, Laos, Miaos, Mons, Tais, Akhas, Yeos and other tribes moved south through the river valleys as Chinese power consolodated. 
The story of the Mekong region is written by the tapestry of people who have made it their home. The area has served as a land bridge between Asia, Australasia and even the West. First there were the Melanesians who later moved south to islands such as New Guinea. A migration of Mongoloids from China and Tibet began in about 5,000 BC.
The ancestors of present-day Malays, Dais, Bais, Khymers, Mons, Burmans Viets, Hmongs, Kadais, Laos, Miaos, Mons, Tais, Akhas, Yeos and other tribes moved south through the river valleys as Chinese power consolodated.
Indian traders arrived in search of gold and spices during the 1st century bringing their Hindu-Buddhist culture.
Western Colonials came later.
Most descendents of the original immigrants have mixed into the modern social fabric of the region, while other have remained isolated and retain their unique cultures, customs and dress.