The Aztecs were a Mesoamerican civilization that flourished in central Mexico from about 1300 to 1521. The Aztec people included different ethnic groups of central Mexico, particularly those who spoke Nahuatl. 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, Tetzcoco, and Tlacopan. 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 pre-Hispanic era, as well as the Spanish colonial era (1521–1821).