What aspects of Mexica society made them vulnerable to attack with the arrival of the Spanish in the sixteenth century?

The constant infighting between Huascar and Atahualpa made the Mexican society internally very weak. This aspect of the Mexican society made them vulnerable to attack with the arrival of the Spanish in the sixteenth century. The Mexican society was so vulnerable that they would have been defeated by any other country willing to take control during the sixteenth century. There was also the difficulty of controlling the diseases that were attacking the people of Mexico during that time. It is also true that the Mexican army was far inferior to the Spanish army.