In 1211, after the conquest of Western Xia, Genghis Khan planned again to conquer the Jin dynasty. The commander of the Jin dynasty army made a tactical mistake in not attacking the Mongols at the first opportunity. Instead, the Jin commander sent a messenger, Ming-Tan, to the Mongol side, who defected and told the Mongols that the Jin army was waiting on the other side of the pass. At this engagement fought at Badger Pass the Mongols massacred hundreds of thousands of Jin troops. In 1215 Genghis besieged, captured, and sacked the Jin capital of Zhongdu (modern-day Beijing). This forced the Emperor Xuanzong to move his capital south to Kaifeng, abandoning the northern half of his kingdom to the Mongols. Between 1232 and 1233, Kaifeng fell to the Mongols under the reign of Genghis' third son, Ögedei Khan. The Jin dynasty collapsed in 1234, after the siege of Caizhou.