How the Spanish Conquered the Aztec Empire: Exploiting Fatal Weaknesses

Hernán Cortés's victory (1519–1521) hinged on five intersecting vulnerabilities of the Aztec (Mexica) Empire:

1. Internal Division: Subject peoples (Tlaxcalans, Texcocans, others) hated Mexica tribute demands and human sacrifice quotas. Cortés turned them into a massive allied army.
2. Immunological Naivety: Smallpox (1520) killed ~40% of Tenochtitlan's population, including Emperor Cuitláhuac, shattering leadership and morale.
3. Technological Asymmetry: Steel swords, crossbows, arquebuses, steel armor, and—crucially—horses gave Spanish forces shock power the Aztecs couldn't counter.
4. Religious Misinterpretation: Moctezuma II's uncertainty whether Cortés was the returning god Quetzalcoatl caused fatal hesitation—allowing Spanish entry into Tenochtitlan unopposed.
5. Strategic Alliances: Tlaxcala alone provided thousands of warriors, porters, intelligence, and a secure base—without which Cortés's few hundred men would have been annihilated.

It was not Spanish superiority alone, but the confluence of Aztec structural flaws that enabled conquest.