The Europeans were interest in Africa for two main reasons, slaves and resources. They needed the west African coastline for slave trading since that's where all the slaves were taken by their captors to be sold, and they needed to go deeper into the continent to get natural resources. Central and Southern central Africa were places with things like Gold, but they also needed the subsaharan area for things like Ivory from elephants. They were also looking for things like diamonds.
The borders were created without any regards for people living there which meant that tribes would often be separated and clustered with other tribes that didn't have their cultural beliefs, or didn't even speak the same language. This caused a lot of civil wars because after the colonization, the borders remained, so different ethnic tribes would fight for power over the other tribes.
