Whether or not the myth is true, we do know that the Aztec established Tenochtitlán by 1325. By the 1400s, the Aztec civilization had begun to expand. The Aztec proved to be fearsome warriors. One by one they conquered neighboring city- states and added them to their empire. By the early 1500s, the Aztec Empire included four hundred to five hundred city-states and controlled much of present-day Mexico. The Aztec emperor ruled more than five million people. Tenochtitlán alone probably had between 150,000 and 200,000 residents, making it one of the largest cities in the world at this time. No city in the United States would grow so large until the 1800s.

The Aztec were well-known warriors. By conquering other people, they were able to gain wealth. Aztec warriors then forced conquered peoples to send their gold, silver, jade, and turquoise to Tenochtitlán. Those who had no valuables could send food, cloth, or other goods. People who lived by the ocean might also have to send seashells, fish, or turtles. Farmers might send corn, beans, peppers, squash, or fruit. Groups with access to specific environments might have to give animal skins and feathers. Craft-working communities might send pottery or blankets to Tenochtitlán.