From the 2006 Nigerian census figures used by the government for budget planning and policy making, the Igbo ethnic group in South East among the major ethnic group in Nigeria due to her numerical strength has become a minority ethnic group in Nigeria. This trend in ethnic density of Nigeria especially the Igbo ethnic group is detrimental as population largely determines who gets what in Nigeria especially when it comes to elections and resource Control. Currentlythe Igbo ethnic group is facing marginalization of all sorts due to the population density of Igbo ethnic group.This studyis aimed at investigating how colonial administration led to the negative trend in ethnic density of Nigeria that led to the marginalization of the Igbo ethnic group in Nigeria's fourth republic. The study made use of Post-Colonial Theory as a framework of analysis. The methods for this research is as follows,ex-post facto research as its research design; content analysis as it analytical technique; secondary source as its data collection base. Hence all data collected were qualitatively synthesized thoroughly to ensure coherence and objectivity. Result showed that, colonial Administration led to the negative trend in the Igbo ethnic density that led to the marginalization of the Igboin Nigeriathrough population census manipulation, slave trade, alien religion, cultural domination in Igboland and destruction of Igbo economy. The study recommended among others that: Igbo political elites should improve the economy and standard of livingof people in South East by establishing industries, free education, free health care, electricity, and other social amenities to encourage the Igbo ethnic group outside South East to come back to their states.
Keywords: administration, colonial, density, ethnic, fourth, group, igbo, marginalization, nigerias, republic, study