The Aztec Triple Alliance, or Aztec Empire began as an alliance of three Nahua city-states or "altepeme": Tenochtitlan, Texcoco, and Tlacopan.

These city-states rule the area in and around the Valley of Mexico from 1428 until they are defeated by the Spanish conquistadores and their native allies under Hernán Cortés in 1521.The Triple alliance is formed from the victorious faction in a civil war between the city of Azcapotzalco and its former tributary provinces.

Despite the initial conception of the empire as an alliance of three cities, Tenochtitlan quickly establishes itself as the dominant partner By the time the Spanish arrive in 1520, the lands of the Alliance are effectively ruled from Tenochtitlan, and the other partners in the alliance have assumed subsidiary roles.The alliance wages wars of conquest and expands rapidly after its formation.

At its height, the alliance controls an empire that covers most of central Mexico as well as some more distant lands.

Aztec rule has been described by scholars as "hegemonic" or "indirect".

Rulers of conquered cities are usually left in power as long as they agree to pay semiannual tribute to the alliance or provide military support in wars with enemy states.