I’m going to have to disagree with that, based on what I’ve read. I haven’t read Guns, Germs, & Steel, but my guess is that I’d disagree with that as well, at least in part.
I would recommend reading A History of Warfare by John Keegan. He is an eminent military historian, and when I first started wanting to learn about military tactics & strategy, this is the book I was directed to. It is very readable, and very interesting.
The notion, as partly eluded to above, is strictly cultural. The Persians didn’t stand a chance against the Greeks. Not because they were technologically backward, but because the Greeks had learned to fight with fatalistic resolve, seek a decisive decision, and to operate with great coordination. They threw themselves into the enemy ranks with total abandon, minds set, not on surviving, but on killing the enemy there and then. The Persians were much more hesitant and “timid,” for lack of a better word. They were unprepared for what was to come.
Very few Native American cultures had a sense of cohesion or attitude toward warfare that matched what had developed in Europe (and elsewhere). Many South Americans (I’ve forgotten which empire was in S.A.) were familiar with warfare en masse; however, it was for getting prisoners rather than dominating another society. In North America, many, if not most, of the cultures used no battlefield tactics and treated warfare as a sort-of full-contact sport. I have no doubts that even if it were the Native Americans who had the steel, the Europeans would have dominated them because of their cultural attitudes toward warfare. Compare two fit individuals. One has a steel breastplate, a low-tech metal helmet, and a rapier. The other has a loincloth and a baseball bat. The first man’s purpose is to look good in battle to impress his friends and, if he can, injure the second man enough to take him prisoner. The second man, however, has abandoned his life to Fate and is solely concerned with killing the first man. Who would you put your money on?
If you can find a copy of it, Harry Turney-High’s Primitive Warfare is a fascinating discussion of the subject.