Take a gander at this.
Comparing the size of African economies to those of English counties. London roughly equals Nigeria for example, the Seychelles the Isle of Wight, Zimbabwe Northumbria.
One point to be made being that we would consider someone entirely mad if they tried to suggest trade barriers in between English counties. Or infant industry protection for them, or self sufficiency of them. yet entirely serious people do suggest exactly the same for African countries and we let them get away with it.