Goddard, Stephen. Ago That became Oyo: An Essay in Yoruba Historical Geography. The Geographical Journal (Blackwell Publishing). Jun 1971, 137 (2): 207–211. JSTOR 1796741. doi:10.2307/1796741.
Smith, Robert S. Warfare & Diplomacy in Pre-Colonial West Africa Second Edition. Madison: University of Wisconsin Press. 1989. ISBN 0-29912-334-0.
Stride, G.T. & C. Ifeka. Peoples and Empires of West Africa: West Africa in History 1000-1800. Edinburgh: Nelson. 1971. ISBN 0-17511-448-X.
Thornton, John K. Warfare in Atlantic Africa 1500-1800. London and New York: Routledge. 1999. ISBN 1-85728-393-7.
Thornton, John. Africa and Africans in the Making of the Atlantic World, 1400-1800 (Second Edition). Cambridge: Cambridge University Press. 1998: 340 Pages. ISBN 0-52162-724-9.
Easley, Dr. Larry. "The Four Forest States of Africa." Oyo Empire. Southeast Missouri State University, Cape Girardeau. 2 Mar. 2009.