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

Slavery and lacks of resource

Explanation:

In order to Obtain their Slaves to sell , many Europeans in the past Started establishing '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.

In order to fulfill the demand made by the European, many African leaders started ordering their people to attack people from other tribes and capture them. They sold these captured tribe members as Slaves to the European Traders. The attack created hatred among the tribes and caused Political and ethnic rivalries within countries in Africa.

On top of that, The harsh climate In African region made it really hard for crops to grow and water to be reserved. This made people from different tribes constantly fought one another to obtain the scarce resources.