The Spaniards easily conquered the Aztecs and the Incas, et al; because up to that period of time, there were no horses, pigs, cows, and other domestic animals on the continent which had pre-innoculated them to have resistance or immunity to certain diseases.
Perhaps the Indians were savages and subhuman and evil.
Maybe, but they were not going out of their way to disrupt the world by terrorizing innocent people everywhere.
I do not care for your analogy that American Indians were as despicable as are the real sub humans who nowadays go by the name Ayatollah, Imam, or whatever leadership nomenclature of that rotten cult.
At least in the case of Aztecs there was another reason. Aztec rule was quite nasty and for their Indian serfs the Spanish rule represented the huge improvement. So the majority of population sided with the new masters.
If you were given the choice between Aztec and Spanish rule whom would you prefer?
In general Spaniards with their feudal/Catholic mentality were looking for subjects so they could have the comfortable status of hidalgos (aristocrats) in the New World. That way the Spanish/Indian two class societies were formed and after passing of time they started to mingle. For example most of today Mexicans are Mestizo.
The self-reliant Anglo Protestants on the other hand had not much use for Indians. It was more convenient if the savages went out of the picture.