Not to discourage further answers or discussion, but from /r/askhistorians FAQ:

The native americans and several other cultures did not experience the same technological advancements as europe. What has caused this diffrence? (/u/snickeringshadow's 2-part answer here is really fantastic)

Why did European, Middle Eastern and Asian societies develop far more technology than indigenous civilizations in the Americas?

Why didn't Native Americans advance nearly as quickly as Europe?

Why is Africa "less developed"?

What about the Mali, Ghana, and Songhai empires? I don't remember much about the great Caliphates, but the Abbasid's invented hospitals.