Touchy question, I know. I guess I'm looking for a reason why they remained so tribal and never advanced beyond spears/slings or in other technological areas like architecture or education.

As I see it, after ancient times Africa was mostly left alone as the middle east, southeast Asia, China, Japan, and Europe developed some amazing technology. All the places had plenty of people and resources, Africa being rich in many valuable resources to iron and bronze age peoples. They all also had warfare as a driving force for advancing technology. Why did they not develop advanced skills or trades to produce high quality weaponry? Why didn't they develop better building materials, why didn't they learn to exploit valuable resources?

What reasons are accepted by historians for the low technological state that Europeans found among the African tribes at the beginning of the Scramble for Africa (early 19th century).

Note: I realize Egypt and parts of northern Africa were technologically advanced from an early part as parts of the Greek and Roman empires. I'm more referring to sub-Saharan Africa.