Yes, that answer is partially correct. The kings of Ghana, also known as the Wagadou Empire, became wealthy through controlling and taxing the trans-Saharan trade routes that passed through their territory. Ivory was indeed one of the valuable commodities that traders transported along these routes, which contributed to the wealth and prosperity of the Ghanaian kings. Additionally, they also profited from exchanging other commodities such as gold, salt, slaves, and various agricultural products.
