Religion: The cultures of Americans, like that of the Spaniards, were deeply theocentric. In that case, it was not fundamental who had more men or less but who benefited more Heaven. the Spaniards gave the impression to the Indians that the Christian god was on their side and many Indians lost the reason to continue fighting
The horse and other animals: that was total and totally unknown by the American Indians
Technology: they were technologically more backward than the Spanish
Human resources: the capacity of man was differential in training of war
writing: they belonged to a literate society that, thanks to writing, had at its disposal an enormous corpus of knowledge about human behavior and history.
Diseases: infectious diseases endemic in Eurasia, In some people there was gangrene in the body and the victims bleeding from the ears.
