How did the west African kingdoms become wealthy select the best answer from the choices below

Ghana's rulers gained incredible wealth from trade, taxes on traders and on the people of Ghana, and their own personal stores of gold. They used their wealth to build an army and an empire. Extensive trade routes brought the people of Ghana into contact with people of many different cultures and beliefs.

Explanation:

a historian researching the immigration policies of the early 1900s would expect a source written today,rather than in 1910 to :

( a ) be more interested in objective data and statistics.