How did the Aztecs build on the achievements of earlier Mesoamerican cultures and develop new traditions to create their large empire?

According to their oral tradition, between 1300 and 1345 a group of Nahuatl-speaking people, the Mexica, migrated southward from what is now northern Mexico, settling on the shores and islands of Lake Texcoco in the central valley of Mexico (Map 11.5). They formed a vast and rapidly expanding empire centered around the twin cities of Tenochtitlan (tay-nawch-TEET-lahn) and Tlatelolco, which by 1500 were probably larger than any city in Europe except Istanbul. This was the Aztec Empire, a network of alliances and tributary states with the Mexica at its core. Examining the means by which they formed and expanded their empire, as well as the vulnerabilities of that empire, can help us build a rich understanding of Mesoamerican society.