The Aztec Empire was known as an alliance between the three city-states of Mexico: Tenochtitlan, Texcoco, and Tlacopan from 1428 to 1521. Also known as the “Triple Alliance,” these three city-states oversaw the area in and around the valley of Mexico and controlled most of central Mexico. In 1521, Spanish conquistador Hernán Cortés led an expedition into the region that precipitated the fall of the Aztec Empire and marked the beginning of the Spanish colonization of the Americas.