What were the causes of the 1975 military coup de'tat in Nigeria?

On 29 July 1975 the government of General Yakubu Gowon was overthrown in a bloodless coup that brought General Murtala Muhammed to power. The coup was caused by a combination of the following factors.

1. Failure to hand over power to civilians: Gowon had promised in 1970 to return the country to civil rule by 1976, but in 1974 he reneged, declaring the date unrealistic. This broken promise angered many Nigerians and members of the armed forces.
2. Corruption and indiscipline in government: Widespread corruption, indiscipline and abuse of office by public officials, including some of Gowon's own military governors, discredited the administration.
3. Indictment of the state governors: Most of Gowon's twelve military governors were widely accused of amassing illegal wealth and gross misconduct, yet he failed to call them to order or remove them.
4. Economic mismanagement: The government was accused of mismanaging the economy despite the oil-boom revenues; the notorious Lagos cement armada (the port congestion scandal) was a glaring example of waste and poor planning.
5. Insensitivity to public grievances: The administration appeared aloof and unresponsive to the hardships and complaints of the people, including delays over a census and the general drift of government.
6. Slow pace of decision-making and drift: Gowon's style of endless consultation and indecision created a sense of drift and inertia in the government.
7. Discontent within the army: Grievances over promotions, welfare, prolonged military engagements and the general conduct of affairs bred discontent among sections of the armed forces.
8. The 1973 census controversy: The disputed and inconclusive national census heightened political tension and further weakened confidence in the regime.
9. Loss of credibility and public confidence: The combination of these failures eroded the legitimacy of the Gowon administration and made its overthrow acceptable to many Nigerians.

These accumulated grievances provided the justification for the July 1975 coup that ended Gowon's nine-year rule.