The correct answer to this open question is the following.
The Aztecs build such a powerful, rich state because they were fierce warriors, well trained that formed an unstoppable army and conquered many other cultures. When Aztecs conquered other tribes, these tribes had to pay tribute to the Aztecs. That is why they get so rich. For instance, they force other tribes to pay tribute such as the Tlaxcanteans, (nowadays the state of Tlaxcala) and the Chollulans (nowadays the state of Puebla) southeastern and south Tenochtitlan, the Aztec capital city (nowadays Mexico City).
