Qing Emperor Taizhong (太宗) led an invading force of 130,000 onto the Korean Peninsula in the 12th moon of 1636. King Injo originally planned to flee the capital and take refuge on Ganghwa Island, but the situation deteriorated rapidly. The king heard a report that an advance Qing force was descending on the island, and he hastily headed for Namhan Mountain Fortress without bringing provisions. Rescue troops were raised around the kingdom, but they were crushed before they could reach the fortress, which was left isolated and without support.
News that Ganghwa Island had fallen reached the court officials at Namhan Mountain Fortress, and they lost their will to resist further. On the 30th day of the first moon in 1637, King Injo left the compound to surrender to Emperor Taizhong.
At the time, the Joseon army at Namhan Mountain Fortress totaled a mere 12,000 men, meaning they were outnumbered by more than ten to one. The Qing soldiers were also much better trained. Despite such overwhelming odds against them, the Joseon side managed to resist for 47 days.