The Spanish had a distinct advantage in weaponry over the Aztecs. They had guns, which were much more powerful than the Aztecs' bows and arrows. They also had steel armor, which protected them from the Aztecs' obsidian weapons.
Disease
The Spanish also brought diseases with them to the Americas, such as smallpox and measles. These diseases devastated the Aztec population and weakened their ability to fight.
Political disunity
The Aztec Empire was not a unified political entity. It was made up of a number of different city-states that were often at war with each other. This made it difficult for the Aztecs to mount a coordinated defense against the Spanish.
Alliances with indigenous groups
The Spanish were also able to form alliances with indigenous groups who were unhappy with Aztec rule. These alliances provided the Spanish with additional troops and support.
So, the correct answer is Superior weaponry.