What factors led to the conquest of Native Americans by the spanish?

Answer 1

They had guns, armor and horses. The native tribes had never seen any of them before. Also the natives were not all united. For instance the Spaniards had Indian allies who had been brutalized by the Aztecs. But perhaps the most important thing was that the Spaniards were immune from the diseases that killed the natives in great numbers. They seemed to be gods.

Answer 2

Guns, Germs, and Steel.