In the 1800s to early 1900s countries in Africa were invaded and all of their natural resources like gold and silver. this has slowed their growth as they have few resources
Because of this lack of resources has slowed and stopped the industrial revolution from occurring in Africa as thoroughly.
This has left the poor countries lacking behind the other countries and the poorer countries are left to deal with corruption and unrest. Whilst the rich countries sell the resources for a large profit.