The origin of the Nias people is unknown. There are striking cultural similarities with the Batak, Toraja, Ngaju Dayak, and peoples of eastern Indonesia, all of which belong to the same language family. But similar social systems can be found among peoples of highland Southeast Asia (Kachin, Chin, Naga). A diffusion of so-called megalithic cultures from Assam has been postulated, but more comparative research is needed to substantiate reconstructions. There is a myth of origin from the center of Nias, and clan pedigrees all connect ultimately to a few tribal progenitors. The great cultural variation in Nias cannot easily be explained therefore by a theory of separate waves of migration to the island. The only important external contact recorded before Dutch intervention is with Acehnese slave traders who brought gold, the supreme prestige object, needed for bride-wealth and feasts of merit. The slave trade led to the depopulation of large areas, and was only brought under control in this century. In 1857 the whole island came nominally under Dutch control, but Nias remained marginal to colonial interests until a change in policy toward the Outer Islands, which led to the complete conquest of the island in 1906. Traders from Sumatra, some of whom settled in the port of Gunung Sitoli, brought Islam to many coastal areas. Christianity was introduced by German Protestant missionaries in 1865, its geographical spread coinciding with colonial domination. It made little progress, however, until the traditional social structure and its ideological underpinnings were broken down by missionary and government interference, paving the way for a wholesale rejection of tradition. From around 1915 a series of apocalyptic conversion movements swept across the island. The character of Christianity in Nias today and its relation to traditional culture owe much to this period, which has come to be known as The Great Repentance. Postindependence Nias has seen some economic development and expansion of the administrative capital and an increasing centralization of power away from the villages.