Every nation that ruled its era had a few things in common on the road to becoming great and one of the cornerstones is the rule of law.
Basically they had an agreed upon code of law and rules that in theory everyone from the beggar on the street to the king was subject to.
The Persian empire stood hundreds of years at times because even though the king's word was law, they were carried out evenly among all peoples (in theory). Romans had Roman Law that protected everyone. The reason why the gospel could spread was because Paul was a Roman citizen and it protected him from from arrest when he was speaking the word to various areas. Jesus was not a Roman citizen so he could be crucified. Paul couldn't under the same standard. The British had English Common Law and the US has the constitution.
Now, I say 'in theory'. Of course these laws were violated but the masses believed in them and that's what counted to keep stability. Once the masses stopped having faith in it for whatever reason, society deteriorated.
That said, the various African countries have changed, altered, or completely ended their various constitutions in their brief history. My grandmother is older than most African countries. Yours probably as well. In that time new regimes, etc, have happened and they change it, etc.
For Africa to become stable, you MUST have the rule of law that is not just fair, it must be accepted by the masses and the masses must hold those in power accountable to it and finally, and this is probably the most important. The military must adhere to it.
If you have that, the tribalism is not as effective.