Canton System
First imposed to deal with Japanese piracy amid the mopping up of Yuan partisans, the sea ban was completely counterproductive: by the 16th century, piracy and smuggling were endemic and mostly consisted of Chinese who had been dispossessed by the policy. China's foreign trade was limited to irregular and expensive tribute missions, and the military pressure from the Mongols after the disastrous Battle of Tumu led to the scrapping of Zheng He's fleets. Piracy dropped to negligible levels only upon the end of the policy in 1567, but a modified form was subsequently adopted by the Qing. This produced the Canton System of the Thirteen Factories, but also the opium smuggling that led to disastrous First and Second Opium Wars in the 19th century.