Mankind progresses greatly when mobility enables exchanges, often trough trade, which achieves wealth and progress in culture and technology. The Roman roads mainly served to control a growing empire militarily, achieving the Pax Romana. The Silk Road enabled major east-west exchanges, not just Chinese silk for European silver, but also inventions, ideas and alas pestilence, yet the Mongol empire conquered by Genghis Khan allowed unprecedented interaction in the greatest of the migrations of steppe tribes caused by famine, then drought on the Mongolian pastures. The process advances spectacularly thanks to transport innovations, like railroads opening up large parts of North America. Modern technology tops it all, with communications without travel, evens satellites and Internet.
—KGF Vissers