I think an overarching understanding that this video helped explain to me of of the three empires that each played an important part in this region's history and that kingdom borders waxed and waned and don't follow today's political borders necessarily.  This is definitely a Western construct that limits one's understanding of what exactly a border is.  

The three empires are The Ghana Empire, The Mali Empire, and The Songhay Empire.  Another significant understanding is that control of the trade routes dictated so many things: power, wealth, spreading of religion and control.  The routes that could maintain through the Sahara were key and the domestication and breeding of camels a game changer.  During the Ghana Empire, chiefs still had autonomy over their tribes as long as they paid tribute (and taxes) to the King.  Koumbi Saleh even kept the chief's sons as a token of allegiance.  Traditions tied to the coast and rivers (fishing) as well as herding and farming sustained.  Iron technology was present and ceramics since the 9th century have been found.  

At one time copper was more valuable than gold and salt almost equal to the value of gold in weight.  In fact, gold was traded for rock salt in the form of bars, mined outside the Ghana empire.  It was sought as a spice but also for medicinal uses.  

I found it interesting that Islam brought education, a written language, and that books and libraries are still valued and preserved.  Teachers and academics had books.  Now the books are in museums, written in Arabic and although many are the Koran, there are still histories and biographies preserved.  

In general it seems the transition from one empire to another was a relatively quick transition.  As Islam became more common, it's effects became more prevalent.  Mansa Musa, a most famous ruler, began a pilgrimage to Mecca  with 60,000 + in tow.  He stopped in Cairo, was probably the wealthiest King at the time (monetary) and brought writers and poets back from Mecca, thus more influencing his empire with Islamic thought and practice.  Through all this history we are reminded that Africans never lived in isolation.  People were always on the move.

All of this is important to know as we continue to explore the diversity, the influence and implications for today, the history that spans way before outside influences, and how this history influences the people of Africa today, not as a whole, but individually or at least by region.  These African empires were known throughout Europe and the Indian Ocean way before colonialism began.