The spreading of disease was a great ally of the Spanish during the Mexican conquest. Europeans came to america carrying a number of conditions that had never been in touch with the indigenous population of the Americas. This meant that the consequences were disastrous for the natives as their immune systems did not have the proper antibodies to fight off the infections. In a 20-year-long period since the arrival of Columbus and his men, millions of natives had been wiped from existence due to illnesses that came from Europeans and from enslaved Africans that were brought to the Americas in their ships.
The natives were affected by a variety of conditions, such as the flu, smallpox, malaria, tifus and yellow fever. These diseases decimated their population and made it easier for Spanish conquerors to enslave and slaughter the Aztecs. Many historians currently believe that it is plausible that disease had killed more people than any armed conflict that occurred between natives and invaders.