The two most important trade items were gold and salt. In west Africa they had their supply of gold but not salt. So they get the salt from the deposits in the Sahara.
For the Empire of Ghana to survive, they relied heavily on trade.
This is the king of Ghana...
I am the King that made Ghana prosper. I was able to hold power within the empire by maintaining a large army.
Then the Ghana rulers converted to Islam. This eventually help the empire because Muslim advisors were helping the king run his kingdom
Until one day in 1076 when the Muslim Amoravids of North Africa completes the conquest of Ghana. After that, Ghana had lost the gold- salt trade and many other resources and couldn't get back on its feet again.
After the Ghana never regained its power, in 1235 the kingdom of Mali had began.