The Aztec Empire, also known as the Triple Alliance (Classical Nahuatl: Ēxcān Tlahtōlōyān, [ˈjéːʃkaːn̥ t͡ɬaʔtoːˈlóːjaːn̥]) or historiographically as the Tenochca Empire, was an alliance of three Nahua city-states: Mexico-Tenochtitlan, Tetzcoco, and Tlacopan. These three city-states ruled that area in and around the Valley of Mexico from 1428 until the combined forces of the Spanish conquistadores and their native allies who ruled under Hernán Cortés defeated them in 1521. Its people and civil society are historiographically referred to as the Aztecs or the Culhua-Mexica.
The alliance was formed from the victorious factions of a civil war fought between the city of Azcapotzalco and its former tributary provinces. Despite the initial conception of the empire as an alliance of three self-governed city-states, the capital Tenochtitlan became dominant militarily. By the time the Spanish arrived in 1519, the lands of the alliance were effectively ruled from Tenochtitlan, while other partners of the alliance had taken subsidiary roles.