In the Valley of Mexico as group called the Teotihucuans and they built an enormous capital city. When they collapased a new group called the Toltecs came and they built a number of cities. They also had a capital called the Tollen with lots of pyramids. Then they were taken over, but they kept their religion.
Then anotherr group came that called themselves the Mexica or the Aztecs. When settling in the valley he started to influence the Teotihucuans and the Toltecs.
From then on they helped to get spread the empire. Although a group came and made the Aztecs move away and the became Menecaries.