It's not that there was no trade, but rather there is no documentation. The civilizations of the Orient were built largely on trade, and thus had sophisticated

It's not that there was no trade, but rather there is no documentation. The civilizations of the Orient were built largely on trade, and thus had sophisticated accounting systems and wrote everything down. So we have a lot of surviving accounting. And lots of kingdoms were all minting their own coins, so we can find surviving coins in all sorts of archaeological sites that show the travel of money. And the value of trade matters, too. It's not just sub-Saharan Africa that seemed like a backwater. Most of Europe was a backwater, too, outside of Italy and Constantinople (which is only half-European, really). Trade routes were weak there because they just didn't have much to offer in exchange for the valuable silks, porcelain, spices, and other luxury goods of the East. The Vikings were the only big traders of Europe, and their primary product was slaves, captured from impoverished backwaters like Great Britain and Germany.