I am making a historical mod for CK2 (crusader kings 2) with the main focus being on the mongols. And I am wondering in how far they would usurp/destroy the existing political structure after having conquered it.

Historically ,did they destroy all the nobility of for instance Khwarezmia/Jin/Sung, or did they leave a skeletal structure just strong enough so they knew how to steer the country they just invaded?