The Bantu expansion

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The spread of the Bantu languages from a homeland in the Nigeria–Cameroon borderland across central, eastern and southern Africa, and the largest single linguistic dispersal on the African continent. It is usually placed as beginning in the third millennium BCE and continuing over some three thousand years, reaching southern Africa within the first millennium CE. The homeland is identified by the same diversity argument used for Austronesian: the deepest divisions within the Bantu group, and the position of its nearest relatives within the wider Niger-Congo family, both lie in West Africa, while the several hundred languages spread over the rest of the subcontinent are comparatively shallowly differentiated. The mechanism is argued rather than settled — the association with iron-working and with the spread of particular crops is long-standing, but the relative weight of demographic movement, technological advantage and language shift among existing populations remains open, and whether the expansion proceeded as a single front or as separate western and eastern streams is actively debated. It is the reason a traveller can cross a continent and find related languages the whole way.