In 1235, the Mongols began a campaign that ravaged parts of Gyeongsang and Jeolla Provinces. Civilian resistance was strong, and the Royal Court at Ganghwa attempted to strengthen its fortress. Goryeo won several victories but the Goryeo military and Righteous armies could not withstand the waves of invasions. After the Mongols were unable to take either Ganghwa Island or Goryeo's mainland mountain castles, the Mongols began to burn Goryeo farmland in an attempt to starve the populace. When some fortresses finally surrendered, the Mongols executed everyone who resisted them.

In 1238, Goryeo relented and sued for peace. The Mongols withdrew, in exchange for Goryeo's agreement to send the Royal Family as hostages. However, Goryeo sent an unrelated member of the Royal line. Incensed, the Mongols demanded to clear the seas of Korean ships, relocate the court to the mainland, the hand-over of anti-Mongol bureaucrats, and, again, the Royal family as hostages. In response, Korea sent a distant princess and ten children of nobles.