The Aztecs (/ˈæztɛks/ AZ-teks) were a Mesoamerican civilization that flourished in central Mexico from 1300 to 1521. The Aztec people included different ethnic groups of central Mexico, particularly those groups who spoke the Nahuatl language. Aztec culture was organized into city-states (altepetl), some of which joined to form alliances, political confederations, or empires. The Aztec Empire was a confederation of three city-states established in 1427: Tenochtitlan (the capital city of the Mexica or Tenochca), Tetzcoco, and Tlacopan, previously part of the Tepanec empire, whose dominant power was Azcapotzalco. Although the term Aztecs is often narrowly restricted to the Mexica of Tenochtitlan, it is also broadly used to refer to Nahua polities or peoples of central Mexico in the prehispanic era, as well as the Spanish colonial era (1521–1821).
Most ethnic groups of central Mexico in the post-classic period shared essential cultural traits of Mesoamerica. The culture of central Mexico includes maize cultivation, the social division between nobility (pipiltin) and commoners (macehualtin), a pantheon, and the calendric system. Particular to the Mexica of Tenochtitlan was the patron god Huitzilopochtli, twin pyramids, and the ceramic styles known as Aztec I to IV. The Mexica were late-comers to the Valley of Mexico, and founded the city-state of Tenochtitlan on unpromising islets in Lake Texcoco, later becoming the dominant power of the Aztec Triple Alliance or Aztec Empire which conquered other city-states throughout Mesoamerica. It originated in 1427 as an alliance between the city-states Tenochtitlan, Texcoco, and Tlacopan to defeat the Tepanec state of Azcapotzalco, which had previously dominated the Basin of Mexico. Soon Texcoco and Tlacopan were relegated to junior partnership in the alliance, with Tenochtitlan the dominant power. The empire extended its reach by a combination of trade and military conquest. It was never a true territorial empire controlling territory by large military garrisons in conquered provinces but rather dominated its client city-states primarily by installing friendly rulers in conquered territories, constructing marriage alliances between the ruling dynasties, and extending an imperial ideology to its client city-states. Client city-states paid taxes, not tribute to the Aztec emperor, the Huey Tlatoani, in an economic strategy limiting communication and trade between outlying polities, making them dependent on the imperial center for the acquisition of luxury goods. The political clout of the empire reached far south into Mesoamerica conquering polities as far south as Chiapas and Guatemala and spanning Mesoamerica from the Pacific to the Atlantic oceans.
