Hausa are the tribes in the North of Nigeria and primarily Muslim, the 'Federals' as the bunch in the West, around Lagos are called, used the Hausa to stir up trouble with the Biafrans, (mainly Christians), the Federals, including the Nigerian Army, then moved in and so started the Biafran war because the Biafrans were sitting on a whole lot of oil.
At least that is how it was explained to me when I was out there in 1969.