The Nigerian Civil War (1967–1970), precipitated by deep-seated ethno-political tensions and the attempted secession of the Eastern Region as the Republic of Biafra, remains a pivotal event in Nigeria’s post-independence history. This paper explores the ethno-political dynamics that underpinned the conflict, focusing on the interplay of ethnicity, regionalism, political marginalization, and contestation for state power. Drawing on archival sources, scholarly literature, and post-war policy analyses, the study examines the structural causes of the war and evaluates its enduring effects on the processes of nation-building and national integration in Nigeria. It argues that while the end of the war was marked by the federal government’s policy of reconciliation, reconstruction, and rehabilitation, the legacies of mistrust, uneven development, and exclusionary politics have continued to undermine national unity. The paper highlights how the lessons from the civil war remain relevant to contemporary debates on federalism, identity politics, and sustainable governance in Nigeria. Ultimately, it advocates for a more inclusive, participatory, and equity-driven approach to nation-building as a means of achieving lasting national integration.