Nigeria’s biggest problem is that it’s not a country. Yes, on paper it is, but on the ground it isn’t.
You’ve got people in Lagos shopping at the mall and Facebooking their friends while there are people in Borno State who are shitting in a field and can’t read a stop sign.
The country is FAR too large because it inherited artificial boundaries from the colonial era. The south already tried to secede once, and was only kept in by a war so horrifically brutal that it shocked people into creating organizations like Medicines Sans Frontieres (Doctors Without Borders). And the south is about to commemorate the 50th anniversary of that event with plenty of agitation to secede again.
Nigeria is approximately half Christian and half Muslim. There are dozens of languages spoken divided into three groups. And on top of all that, Nigeria has long-standing cultural/race divisions that fuel the complete lack of cohesion or national identity. Oh, and there are STILL clashes between nomadic pastoralists (herdsmen) and location-bound agriculturalists.
And let’s not even get into the colossally inept system of government that has a weak federal power structure competing against para-statal and local authorities.
If you travel across a country and can’t understand what people are saying, can’t pray at the same house of worship, don’t need to follow the same laws/regulations, can’t recognize the lifestyle, food, and traditions, and can’t recognize your own physical features in the people you see, then why exactly are you going to consider them to be your co-patriot and fellow citizen?
Nigeria is a unified country on paper only.
If you want to improve Nigeria, split it into four separate countries and go from there.