This paper explores the nexus between ethnic nationalism and ethno- religious conflicts and sustainable national stability and development in Nigeria. Although, traditionally, national is misexpressed in national pride and solidarity, sense of identity and a shared desire to repulse foreign rule, in Nigeria, however, it is typified in loyalty to one's ethnicity and religion, deep distrust among the various peoples of Nigeria. destructive contestation for state power, resource control and so on. This shift has given rise to ethnic militias and militant groups warring against state powers and often times against themselves resulting in the eruption of violent conflicts and loss of lives and property. This hinders efforts at democratization, economic and social transformation, national unity, stability and cohesion. This paper, interrogates the growth and development of ethnic nationalism, why ethno-religious conflicts have become a recurring decimal in the political landscape of Nigeria and posits that the problem is deeply rooted in the lack of social justice and inclusion and a perceived sense of marginalization which are products of bad politics and bad governance. Using the structural functionalism theory of social development, the paper, concludes that the convocation of a Sovereign National Conference is imperative and key to the elimination of ethnic nationalism and hence promotion of national stability and development.