Final answer:
The Spanish advantage that contributed to the Aztecs' defeat was immunity to smallpox.
Step-by-step explanation:
The Spanish advantage that contributed to the Aztecs' defeat was immunity to smallpox. When the Spanish arrived in Mexico, they unknowingly brought with them smallpox, a deadly disease to which the Aztecs had no immunity. The outbreak of smallpox devastated the Aztec population, weakening their empire and making it easier for the Spanish to conquer.
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