Why did africa never unify under one political system/state?

Honestly your answer is multi-faceted. Let me take an empirical, and not a religious approach. Why Africa never unified under one political system? Unification implies agreement but this is sadly untrue with the black race. Sad but true, there has never been an agreement among black; I would even say it goes deeper. Let me use the instance of marriage: You see a Yoruba telling his daughter not to get married to an Igbo, and Igbo not wanting an Ijaw (FYI, the mentioned are tribes in Nigeria) and then when you bring the sentiments, tribalism, nepotism to the political arena it makes you livid. If you take a look at the African continent (Not one black country excluded) you will discover that Africa is deeply divided and multi lingual (Nigeria alone has at least some 250 Ethnic groups; I am not talking about subdialect) and this tends to hamper unity which leads to strife and disagreements on every facet of life, not political alone. Compare ethnically homogeneous communities and heterogeneous ones and you will have to agree with me.

There was an excessive number of contrasts in topography, dialect, religion, legislative issues, and different parts of life. The essential political unit was the town gathering, where significant choices concerning the general public were embraced. While some indigenous African political frameworks were more intricate and systematized than others—the purported "state social orders"— every one of them had some type of incorporated power and expert.

Where are the statements?