Alliances (The conquistadors made alliance with tribes who didn’t like the Aztecs)
Weapons (Spaniards had advanced weaponry and horses, to their advantage) The Spaniards had advanced weaponry and horses. These things were unknown to the Aztecs, which caused fear.
Geography- The Spanish blocked Tenochtitlan’s causeways, bridges, and waterways. This cut off water supply, which led to the death of thousands of Aztecs because of starvation.