The Oyo Empire (1400-1830s) was a powerful Yoruba polity in what is today southwestern Nigeria. Situated in an ideal geographic location between the Volta and Niger River, the Oyo Empire became an important trade center. Its foundation myth draws upon Yoruba religious beliefs and holds sacred the original settlement of Ile-Ife, which continues to be upheld as the creation site for the Yoruba people with significance to local religious practitioners as well as members of African-derived religions outside of Nigeria. Increased trade with European colonial powers, internal strife (which provided a constant stream of captives to be sold to Europeans to fuel the transatlantic slave trade), a weakened army, and the growth of Islamic expansionist movements led to the collapse of the Oyo Empire.
Sources:
Toyin Falola and Matthew M. Heaton, A History of Nigeria (Cambridge: Cambridge University Press, 2008).