Bantu peoples is used as a general label for the 300–600 ethnic groups in Africa who speak Bantu languages. They inhabit a geographical area stretching east and southward from Central Africa across the African Great Lakes region down to Southern Africa. Bantu is a major branch of the Niger-Congo language family spoken by most populations in Sub-Saharan Africa. There are about 650 Bantu languages by the criterion of mutual intelligibility, though the distinction between language and dialect is often unclear, and Ethnologue counts 535 languages. Between 2500–3000 years ago, speakers of the proto-Bantu language group began a millennia-long series of migrations eastward from their homeland in West Africa at the border of eastern Nigeria and Cameroon. This Bantu expansion first introduced Bantu peoples to central, southern, and southeastern Africa, regions they had previously been absent from. The proto-Bantu migrants in the process assimilated and/or displaced a number of earlier inhabitants that they came across, including Khoisan populations in the south and Afro-Asiatic groups in the southeast. Individual Bantu groups today often include millions of people. Among these are the Luba of the Democratic Republic of Congo, with over 13.5 million people; the Zulu of South Africa, with over 10 million people; and the Kikuyu of Kenya, with over 6 million people. Although only around five million individuals speak the Bantu Swahili language as their mother tongue, it is used as a lingua franca by over 140 million people throughout Southeast Africa. Swahili also serves as one of the official languages of the African Union.