I would encourage you to encourage your writers not to use the word "tribe" (Pambazuka News 167). For a complete explanation see Thank you for your consideration.

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Tribe does not convey the depth of history, tradition, arts, social structure, cuisine, dress, ethics and rituals that these groups developed. We don't speak of the "tribes of Europe," usually "ethnic group" or nationality is used. Similarly Native Americans had their "nations" and confederations. Another choice is to refer to a "people". Again if possible and appropriate be more specific; "the Hausa people," "the Mande ethnic group," or "the Zulu nation."