Among the mountains of the Malay Peninsula exist to this day small groups of dwarf, black-skinned, kinky-haired people, different from all other races of the country but closely related to the natives of the Andaman Islands and the Negritos of the Philippines; it has been surmised that these Ngo (Semang) are the dwindling remnant of a once numerous population, successors to (and possibly descendants of) the Neolithic men. Following the Ngo and sometime during the past few millennia, it is believed that there came successive waves of a people of Mongolian origin who, making their way down the rivers, drove the primitive Negritos into the hills and settled in their place. Now conveniently known as the Mon-Annam family, their descendants are the Mon (Peguans), the Cambodians, and the Annamese, as well as numerous semibarbarous lesser tribes which persist among the mountains of the subcontinent. Probably between two and three thousand years ago and certainly after the arrival of the Mon-Annam immigrants, another great population wave, known as the Tibeto-Burman family, rolled southward over Indo-China but chiefly descended the valley of the Irrawaddy (where they have given rise to the modern Burmese), thus scarcely entering Siam at all. Only in comparatively recent times, driven from their former homes by political disturbances, have tribes of this stock (Yao, Meo, etc.) migrated into Thailand and the territories to the east, where they are constantly being joined by others of their blood brothers from farther north. While the Mon and the Khmer (Cambodians) were still spreading over the southern parts of Indo-China and before they had begun, under the influence of colonists from India, to emerge from a condition of savagery, the tribes which they had left behind them at different points during their southward movement were already being driven back into the mountains and brought into a state of partial subjugation by the members of a third great family of migrants from the north. These were the people now known as Lao-Tai, who, sending out bands from their ancient seat in the valley of the Yangtze, had already, 2,500 years ago, established a powerful state on the banks of the Me Khong in the neighborhood of the modern Wieng Chan (Vientiane).