Africa must learn from its history and its present time; and also from World’s history and contemporary struggles.
Imperialism Is Utterly Evil whether it is Western; Eastern; Arabic; African; or any other form. The United States of America; The United States of Europe; a United States of Africa; or other Imperialist designs are against the national interests and sovereignty of free nations. Unity is extremely good; but what kind of unity that could be praised?
Unity is like marriage cannot involve abuse; injustice; or violence. Both are contracts between free people with equal rights and they require continuous consent.
Any successful form of government must recognize and adhere to these facts. That is why federation or confederation of nation-states is much better than those grand schemes of elite tyranny, such as the USA; The EU; and a United States of Africa. Unity grows slowly from healthy seeds; and it is not comfortable prison or slavery.
Those African leaders who called for a United States of Africa are trying to straighten a healthy curve and make shortcuts. Tribalism and nationalism are the building bricks for a stronger African continent. There is no good reason to marginalize or defame Tribalism and nationalism and at the same time to call for African; European; Asian; or American Unity.