The Aztec had an army of hundreds of thousands, but they were defeated by a small Spanish force because their calendars had foretold the destruction of their empire and the return of their god, Quetzalcoatl. The ruler of the Aztec, Moctezuma, therefore wanted to obey his god.
The Spaniards rode horses. The Aztec had never seen them before. They thought they were large deer another sign of the arrival of the god.