Weakened from Previous Battles
The Aztecs had been involved in battles with the Mixtec and the Zapotec before Cortes arrived. It is likely that the Aztec armies were weakened by these other battles, making it easier for the Spaniards to defeat them. Not only did previous battles weaken the Aztec armies, but they angered surrounding groups. Some of these groups sided with the Spaniards and helped contribute to the downfall of the Aztec empire.
One of the biggest reasons of the fall of the Aztec Empire, was due to the amount of people being killed as “sacrifices”. There are many ways this led to the fall of the empire: first of all, killing thousands of your citizens cannot be good in any way. Those people and their children that had been killed could have been used in the military to fight against the Spaniards. Another way this led to the fall , was because the Aztecs killed some people from neighboring city-states. Which caused hatred from those city-states , such as the powerful city-state Tlaxcala. At the end, Tlaxcala teamed up with the Spanish to fight the Aztecs.
Another huge reason of the fall of the empire was disease. When Hernan Cortes heard another Spanish Army from Cuba was coming to make sure Cortes was following orders, he didn’t like that at all, so he decided to fight them. Part of that army from Cuba was an African slave who had smallpox, which was a very deadly disease. One of Cortes’ men got the disease and smallpox spread across the population. 25% of the population died from smallpox only. The big thing that brought the Aztec Empire down was that smallpox killed Cuitláhuac , the emperor of the Aztec Empire. When there was nobody to command , the Aztec Empire collapsed quickly.
The Aztec’s had control of most of Mexico. When the Spaniards came, they wanted to take control of the Aztec’s and the Aztec territory. Shortly after the Spaniards came, more Spanish conquistadors arrived that wanted control over the Aztec’s. In the end the Spaniards managed to get enough allies and conquer the Aztec’s.