Concept:Regionalism in Nigeria refers to the creation of regional administrative divisions, which was first introduced through the Richards Constitution.Explanation:Sir Arthur Richard introduced Regionalism in Nigeria in 1946.His constitution divided Nigeria into three regions: Western, Northern, and Eastern Regions.This arrangement marked the beginning of regional administration in Nigeria.It also laid the foundation for the later adoption of federalism in the country.Therefore, regionalism is credited to Sir Arthur Richard.Answer:A. Arthur Richard