"Tell that to the native Americans ..."
This remark reflects a profound historical ignorance and an idealization of "noble savage" status disguised as PC. Let's see, starting with Cortes, myth says he an a handful of conquistadores brought down the Aztecs. Reality was, the Aztecs were detested _cannibals_ (really, no joke, those human sacrifices were governed by a "waste-not, want-not" ethic). Their neighbors hated the ground they walked upon - AND MANY STILL DO. Reality was that Cortez was joined thousands of local indians who allied themselves to the Spaniards. Estimate range from ca. 40K to over 100K took the side of the Spanish.
Or, consider Pizarro. He took on the Incas. Again, history seems to favor this myth that the Spanish did it by themselves, but they arrived during a pause in the expansion of the Inca Empire. The Inca tended to assault a region, and having won, forcibly remove large portions of the population to other areas, similar to the Jewish diaspora but on a larger scale. The conflict between the Spanish and the Inca saw the Spanish joined by numerous "tribes" - the survivors of full-blown civilizations destroyed by the Incas - who happily waged war on the Inca again. There are no good estimates of how many joined in the war, but the Inca Empire was larger than the Aztec's, and their foes were far more sophisticated than many of the societies the Aztecs destroyed.