The Aztec people had a very rigid and well-defined society.
As the Aztec empire grew, these calpulli tribes gradually became political divisions within Tenochtitlan.
Within each calpulli, the Aztec people chose four chief officials.
When Tenochtitlan ultimately became the primary hub of Aztec civilization, its ruler became the ruler of the entire empire.
Specific Aztec people, such as the nobility, warriors, and priests, were responsible for supporting the ruler.
The class system of the Aztec people was very strict.
Aztec people could move down in the system by committing a crime or failing to pay a debt.
Source: Native American Encylopedia