Political and ethnic rivalries within countries in Africa were a result of

A. European countries stopped providing aid after WWII
B. the slave trade across the Atlantic Ocean
C. the United Nations waging war against warlike rulers
D. successful independence movements on the continent

B. the slave trade across the Atlantic Ocean

Explanation:

In order to Obtain their Slaves , many European Traders in the past Started a 'Business Relationship with African Leaders. The European traders will give the African leaders a sum amount of wealth in exchange of their help in capturing their own people.

To fulfill their end of the deals, many African leaders started to attack people from other tribes and take sold them as Slaves to the European Traders. The attack created hatred among the tribes and caused Political and ethnic rivalries within countries in Africa.