Using a historical approach, this chapter examines the introduction of foreign religions; Islam and Christianity into Nigeria in addition to the indigenous religion of the people, all of which constitute the ethno-religious diversity of Nigeria which has overtime snowballed into embroiled conflicts, and shows how it has created emerging issues that is affecting the unity and development of the country. It interrogates resources that mirror the heterogeneous religious and ethnic composition of the country and how lack of sincerity in the management of diversity by leadership and institutions in post-colonial Nigeria has impeded socio-economic development and peaceful coexistence.