The Aztecs fell prey to the same colonization that swept through North and South America after Columbus. They found themselves beset on all sides; on one side, the colonizers brought new diseases with them, which killed off Aztec people in staggering numbers. Smallpox in particular weakened the population and contributed directly to the fall of Tenochtitlan in 1521.
Many of the soldiers who were still alive were sick with smallpox while they were trying to fight off the Spaniards, giving the latter a distinct advantage on the battlefield. On another side, the Spaniards were taking advantage of Moctezuma, who believed that Cortes was the Mayan and Aztec god Quetzalcoatl, who in their mythology had left long ago across the sea with a promise to return someday. This is why he was so ready to obey Cortes’ orders and kill the military commanders, which led to the civil uprising in Tenochtitlan that left an opening for the Spaniards to move in with their superior armor and weaponry and finally conquer the weakened, divided city. After that, they did their best to convert the Aztec people to their own culture and religion, erasing much of what made the Aztecs a single, cohesive society.