The TRUTH is... that the people more or less native to Africa and what is now the United States... were pretty much SEPARATED from other humans thru-out the world, and were insulated from all the technological improvements that seemed to come from the middle east, and europe. So, in THOSE areas, ALL people were influences by the ingenuity of ALL the other peoples... from the discovery of smelting metals, mathematics, the written language, and SO MUCH MORE...
If there was ONE factor that acted to hold back certain people... it was that they were ISOLATED, and NOT that they were INFLUENCED... AND, ONCE again... what the liberals TELL us is the reality... TURNS OUT to be just about 180 degrees WRONG