Which social structure did the aztecs and the incas have in common?

As regards social structure the Aztecs and the Incas changed their structure from kinship (tribe system) to a social hierarchy (nobles). Moreover, 
They had local leaders who were accepted as equals if they pay the corresponding tribute. 
Both were ruled by Emperors and so they were divided into rich and poor social class. 

The theory is land mass basically what they said.