Today, most of Africa, especially the countries that are considered "not North Africa", is extremely poor, there are frequent wars, modern medicine is scarce, and most of the nations are either dictatorships, very unstable, or not powerful enough to do anything against terrorism, extremism and exploitation. I don't know much about African history, but I heard of many thriving and rich societies on the continent. I once heard (even though I don't know where anymore, and this may be really really wrong) that the richest king in history was some African kind whose name I forgot. So how did the continent change from a culturally, politically and economically rich place to the Africa we know today?
It's worth mentioning that Africa is a very large and diverse continent - it is the second-largest and second-most populous continent. Even if we examine the parts that are "not North Africa," that leaves 48 nations across a variety of climates and locations.
There's plenty of diversity among nations as well. While there are major problems facing the continent, especially with regards to equality, corruption, and development, it is not made up entirely of culturally and economically poor nations. If you perhaps narrow this question down to a specific region within Africa, or to a specific nation, e.g. Central Africa, Liberia, etc, it might be easier to develop an in-depth response.
This post by /u/Fjosnisse in the FAQ section might be of use to you as well.
I feel like that's a loaded question. Africa has never not been a rich source of cultural and scientific marvel.