Final answer:
Indian allies such as the Tlaxcalans and Totonacs were instrumental in Cortés's conquest of the Aztecs, providing military support and aiding with internal conflicts against the Aztec rule. The introduction of smallpox by the Spanish further weakened the Aztecs, and translators like Doña Marina played a key role in communication and negotiation.
Step-by-step explanation:
Having Indian allies was crucial for Hernán Cortés's conquest of the Aztec Empire. Allies such as the Tlaxcalans and the Totonacs provided substantial military support, with the Tlaxcalans contributing an estimated 200,000 fighters during the siege of Tenochtitlán. These tribes viewed the Spanish as liberators from Aztec rule which often demanded tribute and suppressed their autonomy. Furthermore, the spread of diseases like smallpox, to which indigenous populations had no immunity, severely weakened the Aztecs and disrupted their society, further tilting the balance in favor of Cortés and his Indian allies. The use of translators, such as Doña Marina (La Malinche), who could speak indigenous languages and Spanish, also facilitated alliances and negotiations that were pivotal to the Spanish success.