What do you think caused the Ming dynasty to change its foreign policies?

The answer in e2020 is

China may have become isolationist because it wanted to protect itself from being invaded again. This may have been because of the Mongol invasions and the Yuan dynasty.

The Wanli Emperor (r. [ 1572 1620) attempted to reestablish Sino-Tibetan relations in the wake of a Mongol-Tibetan alliance initiated in 1578, an alliance which affected the foreign policy of the subsequent Manchu Qing Dynasty (1644 1912) in their support for the Dalai Lama of the Yellow Hat sect. ]