Short answers, pulled from the story.
The word ethnic originates from the Greek term ethnos, which appeared in Homeric Greek to describe any large group of people. Early usage referred to a host of men or a band of comrades rather than a specific cultural identity.
The modern sense of peculiar to a tribe emerged in the 19th century. American English began using ethnic to mean tribal, racial, or national minority groups during the 1930s and 1940s.
Fredrik Barth published Ethnic Groups and Boundaries in 1969, which became instrumental for spreading the term in social studies during the 1980s and 1990s. Barth stressed that ethnicity was perpetually negotiated through external ascription and internal self-identification.
Africa contains over 3,000 ethnic groups and more than 2,000 languages spoken across 54 countries. These languages belong to major families such as Niger-Congo, Afroasiatic, Nilo-Saharan, and Khoisan.
The process resulting in emergence of an ethnicity is called ethnogenesis, a term used in ethnological literature since about 1950. Ethnogenesis involves several generations of endogamy resulting in common ancestry sometimes cast as mythological narratives.