The Aztec Empire or the Triple Alliance (, [ˈjéːʃkaːn̥ t͡ɬaʔtoːˈlóːjaːn̥]) was an alliance of three Nahua city-states: , , and . These three city-states ruled that area in and around the Valley of Mexico from 1428 until the combined forces of the Spanish and their native allies who ruled under defeated them in 1521. The alliance was formed from the victorious factions of a civil war fought between the city of and its former tributary provinces. Despite the initial conception of the empire as an alliance of three self-governed city-states, the capital became dominant militarily. By the time the Spanish arrived in 1519, the lands of the alliance were effectively ruled from , while other partners of the alliance had taken subsidiary roles. The alliance waged wars of conquest and expanded after its formation. The alliance controlled most of central Mexico at its height, as well as some more distant territories within Mesoamerica, such as the Xoconochco province, an Aztec exclave near the present-day Guatemalan border. Aztec rule has been described by scholars as "hegemonic" or "indirect". The Aztecs left rulers of conquered cities in power so long as they agreed to pay semi-annual tribute to the alliance, as well as supply military forces when needed for the Aztec war efforts. In return, the imperial authority offered protection and political stability and facilitated an integrated economic network of diverse lands and peoples who had significant local autonomy. Aztec religion was a monistic pantheism in which the Nahua concept of teotl was construed as the supreme god Ometeotl, as well as a diverse pantheon of lesser gods and manifestations of nature. The popular religion tended to embrace the mythological and polytheistic aspects, and the empire's state religion sponsored both the monism of the upper classes and the popular heterodoxies. The empire even officially recognized the largest cults such that the deity was represented in the central temple precinct of the capital . The imperial cult was specifically that of the distinctive warlike patron god of the Mexica . Peoples were allowed to retain and freely continue their own religious traditions in conquered provinces so long as they added the imperial god to their local pantheons. Etymology and definitions The word "Aztec" in modern usage would not have been used by the people themselves. It has variously been used to refer to the Aztecs or Triple Alliance, the Nahuatl-speaking people of central