Why were we taught in school that Igbo people are easterners?
Answer: It is both an unfortunate parroting by teachers and careless adoption by Igbo educated class. Igbo people come from Southern Nigeria and not Eastern Nigeria. It may be correct to say that the Igbo are found predominantly in eastern Nigeria. However, by saying that the Igbo are easterners, the implication is that the Igbo in western Nigeria, numbering about 2.5 million (Agbor, Ogwashi Ukwu, Ibuzo, Okpanam, Asaba, Orimili, Ndokwa, Anioma, etc) are not Igbos. The best known Igbo anthropologist Professor Mike Onwuejeogwu is from the western part of Nigeria, Chukwuma Nzeogwu, Dennis Osadebe, Okonkwo Adibe (the famous musician), Sony Odogwu, etc. are all from the western part of Nigeria. They are no less Igbo than those who live in the eastern part of Nigeria. The correct answer to your question is "the Igbo come from Southern Nigeria."
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