Final answer:
Mesoamerican tribes who resented the Aztec Empire's demands contributed to its downfall by aligning with the Spanish due to a mutual interest in overthrowing Aztec rule. The Spanish also brought smallpox, which decimated the indigenous population, and used superior military technology to their advantage.
Step-by-step explanation:
Other Mesoamerican tribes played a significant role in the rapid fall of the Aztec Empire. Hostilities towards the Aztecs had grown among tribes that resented the empire's demands for tribute and sacrificial victims. These groups saw the arrival of the Spanish as an opportunity for liberation from Aztec domination. The Totonacs, for example, were one such tribe that greeted the Spanish as liberators. In the backdrop of this political alliance building, the introduction of smallpox by the Spanish wreaked havoc on the indigenous population of Tenochtitlán, including the Aztecs, causing the deaths of thousands and weakening the empire severely by 1521. This biological warfare, combined with the Spanish military tactics and weaponry, which included steel armor and swords as well as horses, gave the Spanish significant advantages over the Aztec's traditional weaponry like bows, arrows, and spears. Additionally, the Spaniards strategically capitalized on discontent among subjugated tribes, effectively undermining the Aztec's power base and enabling their swift conquest.