The ming emperors believed that China had been weakened by its contact with other people, and so they're much more cautious in their trade with outsiders, and much more likely to believe that it was best for China to remold itself in the greatness of the past. Most of China's concerns were land base and remain focus on their own internal affairs, but they did venture into the seas around them because they had highly prized precious goods including silk and porcelain.
