Any city or conquered area would still keep a general air of self-control. After being conquered, the state would be forced to pay tribute to the Aztecs.

 The main social distinction within the empire was between commoners and nobles. The nobles held considerably more rights than the commons, the biggest one being the right to take tribute from the commoners on your land.
Work Cited: https://en.wikipedia.org/wiki/Aztec#Social_structures, https://en.wikipedia.org/wiki/Aztec_society, https://en.wikipedia.org/wiki/Aztec_Empire#Law

  Agriculture, the basis of the aztec economy was successfully accomplished by a series of floating rafts called chinampas, these floating rafts covered in the empire’s staple crops, corn and beans, allowed for mass farming despite the location of their city, Tenochtitlan, being surrounded by water. 

  Tianquiztli, the biggest marketplace in tenochtitlan was the basis of all internal trade of the city, most goods and services in the city, spare for a few specific goods sold on smaller more specialized marketplaces, meaning the vast majority of goods and services passed through the market.
  Cocoa beans, known as cacao by the aztecs, was the most used currency, the quality of the bean determining the value. Quatchi however was used by more wealthy Aztecs for larger and more expensive purchases, the tightly woven fabric being very valuable, and a luxury every family desired and enjoyed.

http://aztec.com/page.php?page=economy