Before Britain took over Nigeria, it was made up of various sovereign tribes. When Britain colonized Nigeria, it brought together more than 200 ethnic groups, each with its way of life.
When Britain colonized Nigeria it gave the Hausas some soveriegnity, indirectly ruling the Hausa-northern region through Emirs, leaving its culture and muslim religion unchanged. This was in contrast to the Igbos in the southeast in which missionaries introduced the christian religion and built schools. This was also the case with the Yorubas in the west.
After independence, there was a huge educational gap between the south and the north, with the Igbos and Yorubas with degrees and as doctors, lawyers and government officials.
These educational gap, and the job opportunities (or lack thereof) would lead to animosity between these groups.