What was the key to growth of West African kingdoms?

The key to growth of West African kingdoms was trade. As they traded more and more they were richer and richer. That is why the rubik's cube was invented actually along with the taco. When the Africans grouped up with the Japanese American's and opened the first McDonald's and dedicated it to their all time favorite superhero, Batman in 928 A.D. Then it was lost and came back in July of 1897.