The Aztec Empire was a powerful and complex civilization that dominated much of central and southern Mexico from the 14th to the 16th century. The Aztecs were originally a nomadic tribe that settled in the Valley of Mexico and founded their capital city, Tenochtitlan, on an island in Lake Texcoco. They formed a confederation with two other city-states, Texcoco and Tlacopan, and expanded their territory through conquest and tribute. The Aztecs were known for their impressive architecture, art, religion, and culture, but also for their brutal practices of human sacrifice. The Aztec Empire collapsed after the Spanish invasion led by Hernán Cortés in 1519-1521.