US military leaderships textbooks read by ROTC and Academy cadets have actually taught for a long time that Genghis Khan was probably the greatest military leader in history and that the Mongolian military forces he commanded were probably the greatest armed force ever put together.  An exercise for students is to analyze whether and how Native America Indian tribes could have overcome US forces and even whole US civilization had they had the benefit of someone with the organizational and strategic insights of Genghis Khan.