Well you mentioned the Native Americans, they had allies here too. Each major tribe was allied with a major power. So if you used it against them, even in that case someone could get a hold of that tech and it could come to bite you in the ass later. Interesting example is the fact that Native Americans in the US were very soon all very well armed by their allies in terms of guns and ammo, and they used the armaments given to them by their allies to attack each other. Life in general is more than capable of cooperating when it is not competing even with beings that have little to do with each other. This in the end is called the Red Queen's race https://en.wikipedia.org/wiki/Red_Queen's_race https://en.wikipedia.org/wiki/Red_Queen_hypothesis.