In terms of some further reading, I actually recommend a work of fiction--Chinua Achebe's Things Fall Apart, which opens up the imaginative possibilities of what political complexities existed before formal colonialism in Nigeria (and echoing /u/chauser67 no way in hell was Africa one single monolithic entity, that's a production of racism), as late as the 1890s.

But to just open up things for discussion--the African continent had its own empires inland and maritime, from the Nri of Igboland (in West Africa) to Ethiopian rulers, to the Zulu and the Kongo, and to Ancient Egypt and Carthage, and of course the Muslim empires--civilizations storied in Greco-Roman mythologies, ruling substantial parts of Mediterranean Europe, and producing incredible Moorish architectural legacies in places like Andalusia in Spain.

All before formal occupation and the Scramble for Africa, which arbitrarily cut up the continent according to how European powers fought over maps and visual fantasies. But even before formal occupation and the Scramble, European coastal presence (and the slave trade) wasn't simply just pillaging and raiding (although a great number of it was). Ethnic groups and kingdoms often sold slaves from opposing groups to the Europeans in coastal regions; indigenous elites took part in that violence (albeit unequally) and exercised their own exploitations. So "Africa" wasn't "peaceful," because nowhere was "peaceful" before the Europeans came in. But European rule steps in and it's an entirely new, volatile, and incredibly destructive can of worms.

This question needs to be considered as to why you are asking the question, but I will go ahead. Africa, a continent larger than all of Europe and far more diverse should be considered in exactly the same light as any other land mass containing human settlement.

Empires, tribes, cultures and states rose and fell for millennium, people fought, lived and co-existed for long before recorded history in "Africa" just as they had in any other continent. Be aware that colourising Africa as a single identity or notion is just laughable. The people living in Mombasa had more in common and easily more contact with people from Gujurat or Oman than they did with people living on the Cape of Good Hope or in the Congo.

What is clear is that the "trouble" represented today in lower economic standards, instability and violence is a direct result of the exploitative and violent European colonization and subsequent de-colonisation, in creating nationstates without necessary infrastructure and often without real considerations as to the actual circumstances on the ground.