Several factors contributed to the Spanish conquest of the Aztec Empire. The strategic alliance between Cortés and local tribes who were subjugated by the Aztecs, such as the Tlaxcalans, provided crucial military support. The devastating effects of European diseases, like smallpox, to which the indigenous populations had no immunity, decimated the Aztec population and undermined their ability to resist. The technological superiority of the Spanish, particularly their armor, guns, and horses, gave them a significant military advantage.