Humm.  Interesting.  Maybe many things, including the horse.  Certainly agriculture as a corner stone.  Maybe even climatic shifts, stressing populations, where only certain traits survived.  

Keep in mind that the first Europeans that came to this land brought a culture not indigenous to Europe, as indigenous European cultures were tribal.   As romans and others swept through Europe over the millennia, they left behind new, changed cultures, which continued to evolve.

As far as military superiority (based on economic largess); the only thing it determines is which cultures are going to survive (for now) and which will be exterminated (sooner).  Just ask those tribal Europeans who encountered the romans a few thousand years ago.