Concept:Regionalism was first formally introduced in Nigeria by the Richards Constitution.Explanation:The 1946 Constitution, named after Governor Authur Richard, divided Nigeria into three regions: the North, East, and West.Each region had its own regional council.This arrangement established the regional framework on which later state creation was built.Therefore, the regionalism introduced under Authur Richard laid the foundational basis for Nigeria’s subsequent state structure.Answer:A. Authur Richard