Question

how did the mongol dynasty continue and expand the economic and political changes begun under the tang and song dynasties?

Answer 1

The style that the Mongols used to conquer was to follow Genghis Khan's policy. They started to attack the Jin Empire and the Western Xia then the southern, allied with the Song dynasty. With this success, the old cities like Kaifeng and Beijing were reclaimed by the Song then were attacked by the Mongols under Kublai Khan.