^"Northeast Africa is neither geographically or climatically uniform. Internally it varies widely in altitude, rainfall patterns, river systems, soil types and vegetation cover. In most historical studies the region is also further divided according to strict cultural and political boundaries. It is unusual, for instance, to compare the Sudan with the countries of East Africa, or Ethiopia with anything but itself. Yet the study of the history of ecological relationships makes possible, at the same time that it requires, a recognition of a broader outline to the region which not only acknowledges, but knits together its diverse range of societies".Johnson, Douglas H.; Anderson, David M. (26 June 2019). The Ecology Of Survival: Case Studies From Northeast African History. Routledge. pp. 1–15. ISBN978-1-000-31615-5.
^Daniel, Kendie (1988). NORTHEAST AFRICA AND THE WORLD ECONOMIC ORDER. Michigan, US. pp. 69–82.{{cite book}}: CS1 maint: location missing publisher (link)
^Project MUSE. (2020). Northeast African Studies. Retrieved March 22, 2020. "This distinguished journal is devoted to the scholarly analysis of Ethiopia, Eritrea, Djibouti, Somalia, and Sudan, as well as the Nile Valley, the Red Sea, and the lands adjacent to both."