Nigeria: Four Regions at the Time of Independence
As Nigeria preparded for independence, the British worked out an arrangement which divided Nigeria into four regions. The Hausa-Fulani were dominant in the north, the Yoruba in the west and the Igbo in the east. In this way each of the major ethnic groups would control its "home region." At the same time the British determined that 52% of the delegates to the national legislature would come from the Northern Region as the price of getting northerners to support independence.
The secession of the Biafran Republic meant that the entire Eastern Region, under Igbo leadership (or domination) seceded from the rest of Nigeria. There was also a short-lived effort by the Mid-West region to secede as the Republic of Benin.