Mongolia has a form of slavery but not what you think. It is more like a caste system:
On the top of the Mongolian society there is the Khan, the Empress, the heir, the Dukes and the Governors.
Then there are the citizens. The upper classes of the citizens belong to two castes:
The ''Warrior Caste'': They are Warriors and live only to fight. They have to train in the Arts of War 6 hours every day.
The ''Religious Caste'': They are the Catholic Priests.
Then there are the Middle classes, who belong in the caste of the ''Trader's''.
Finaly there are the lower classes, the slaves, who work in the farms and in the factories. Those slaves cant marry men or women from other castes. However they are paid for their work.