Zhu Yuanzhang had promoted foreign trade as a source of revenue while he was a rebel .
Zhu Yuanzhang sharply curtailed this with a series of sea bans ( haijin ) once in power .
Zhu Yuanzhang had promoted foreign trade as a source of revenue while he was a rebel , but sharply curtailed this with a series of sea bans ( haijin ) once in power .