The Igbo world east and south of the lower Niger: several hundred autonomous village-groups governed by councils of elders, age grades, title societies and oracles rather than kings. The atlas already draws its few centralised fragments - Nri, the Aro Confederacy, Onitsha's Niger-bank towns - but those were small parts of Igboland; the great majority of Igbo ground was acephalous and, until now, blank on the map.
Not an ending: the Protectorate of Southern Nigeria created in 1900 enclosed Igboland, and the Aro expedition of 1901-02 and the warrant-chief system dismantled Igbo political autonomy - but the Igbo are one of Africa's largest peoples today, and the atlas simply hands the ground to Colonial Nigeria at 1900.
The standard single-volume history of the Igbo, covering the acephalous village-group order as well as Nri and the Aro.
Ethnographic Survey of Africa volume that maps the Igbo sub-groups and their neighbours - the classic extent source.