There were also pressing political and military reasons for giving up on sea power. In the 1430s, the threat was growing by land from China’s old enemies, the Mongols. Out to the north, Ming armies made almost annual expeditions beyond the mountains into the vast steppe lands of Mongolia. Then, in 1449, the Zhengtong emperor was defeated in battle near Beijing and captured by the Mongols. The greatest military fiasco in the Ming period, this led to a massive rebuilding of the Great Wall into the form we see today, as well as a new mood of defensiveness and retrenchment.
