With the abolition of regionalism in 1967, ethnicity became more intensified in Nigeria as the country became more polarized. While regionalism promoted nation building in spite of its abuse as a result of ethnicity, which culminated in the civil war (1967-1970), the latter is mostly an agent of disintegration. However, ethnicity does not necessarily constitute threat to the socio-political and economic development of a state; rather, it is its negative employment. Hence the positive aspects of ethnicity often become insignificant in multi-ethnic states like Nigeria. This paper suggests that ethnicity and regionalism can provide solution to some of the socio-economic problems confronting the country. It thus demonstrates through the study of Odu’a Investment Company Limited (OICL), a regional economic bloc in south west Nigeria that regional integration has the potentials of revamping the economy of the country. It also argues that regional cohesion is a tool for national integration. While the paper argues that Odu’a Investment Company Limited (OICL) as an economic bloc has failed to achieve its raison d’être courtesy of regional atomization, it contends that since the beginning of the Fourth Republic, it has been a unifying factor in south western Nigeria.