To add to the body of the academic field of International Relations (IR), this dissertation provides a precise account of major factors responsible for Nigeria's economic malaise and underdevelopment post-independence. The study relied on data extracted from various academic articles and papers on quantitative studies that specifically focused on the relationship between colonialism and Nigeria’s economic development after 1960. A thematic content analysis was adopted and used to analyze the various articles on the reviewed quantitative studies in order to answer the following question: ‘What are the key factors for economic underdevelopment in post-independence Nigeria?’. Deductively, the study finds that ethnic conflicts, colonial imposition and mainly disarticulation in production, are the main factors impacting negatively on the economic development of post-independence Nigeria.