Background information: This is an excerpt from a 1433 speech by Emperor Zhu Di.
Due to so many unexplained difficulties and bad omens, the Majesty is humbled and concerned. . . . To alleviate the situation, all policies that cause the public inconvenience, if not urgent, should be stopped. . . . Policies temporarily stopped include the voyages to foreign countries, horse trading with the remote western and northern areas.
What Ming political and economic policy does this excerpt provide an example of?