<Tr> <Td_colspan="2"> Other Niger--Congo - speaking populations </Td> </Tr> <P> 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 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 . </P> <P> Around 3,000 years ago, speakers of the Proto - Bantu language group began a millennia - long series of migrations eastward from their homeland between West Africa and Central 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, such as Pygmy and Khoisan populations in the centre and south, respectively . They also encountered some Afro - Asiatic outlier groups in the southeast who had been there for centuries, having migrated from Northeast Africa . </P> <P> Individual Bantu groups today often comprise millions of people . Among these are the Shona of Zimbabwe with 14.2 million people; the Luba of the Democratic Republic of the Congo, with over 13.5 million people; the Zulu of South Africa, with over 10 million people; the Tiv of central Nigeria and Cameroon, with almost 10 million people; the Sukuma of Tanzania, with around eight million people; and the Kikuyu of Kenya, with over six million people . Although only around five million individuals speak the Arabic - influenced 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 . </P>

What were the main reasons the bantu speaking tribes left central africa