Nigeria became independent on October 1, 1960. At the helm of affairs were Dr. Nnamdi Azikiwe as President and Sir Abubakar Tafawa Balewa as Prime Minister. In 1961 the Cameroons trust territories were split in two. The mostly Muslim northern Cameroons voted to become part of the Northern Region of Nigeria, while the southern Cameroons joined the Federal Republic of Cameroon.

Regional and ethnic tensions increased after independence. The censuses of 1962 and 1963 fueled bitter disputes, as did the trial and imprisonment of leading opposition politicians, whom Prime Minister Balewa accused dubiously of treason. In 1963 an eastern section of the Western Region that was ethnically non-Yoruba was split off into a new region, called the Midwestern Region. Matters deteriorated during the violence-marred elections of 1964, from which the NPC emerged victorious.

On January 15, 1966, junior army officers led by Major Chukwuma Kaduna Nzeogwu revolted and killed Prime Minister Balewa and several other politicians among whom were Sir Ahmadu Bello, Sardauna of Sokoto and Premier of the Northern Region; Samuel Akintola, Premier of the Western Region, as well as several high ranking Northern army officers. Major General Johnson Aguiyi-Ironsi became the new head of state.