The Aztecs, Incas, and Chinese, all had well developed civilizations, and they all used labor force or tributary system. All of them though has different systems and requirements in this department.
The Aztecs had lot of conquered people. They required tribute in the form of people for sacrifice. As the Aztecs has Gods that were very thirsty for human blood, in order to not sacrifice themselves, the Aztecs were taking people for the other tribes and sacrificed them.
The Inca system of labor force seem to have been the most just one. In this system, everyone, apart from the emperor, had to work for the good of everyone and for the good of themselves. Everyone lived in same homes, wore the same clothes, and worked the same types of jobs.
In China, the tribute system was based on forced labor of the people that were conquered. They had to work, produce certain goods, and give part of those goods or part of the profit from those goods to the governing bodies.
They had their own governer didn't they?
So they could get more resources faster like silk and spices.
