a similar highly audacious approach that they had employed in Khwarezm (1219) and Xi Xia (1226). The Mongols divided into three armies, one to attack Henan from the North in the center of the Yellow River, another to attempt to cross the Yellow River in Shandong in the east, and the last, under Subutai and Tolui, invading the Song Empire and attacking Henan from the more exposed south. The Song initially refused to allow the Mongols passage through the rugged Qinling mountains, so Subutai dodged their forces and isolated the mountain citadels one by one. Disheartened by the ease of the Mongol advance against their strong fortifications, the Song agreed to supply guides. This time Subutai was able to outmaneuver the Jin armies and cross the Han River to invade Henan from the south. The main Jin army promptly marched to intercept Subutai's army at Mount Yu. Its commander, Wan Yen Heda attempted to ambush the Mongols, but the ambush was detected. In turn, the Mongols attempted to draw him into their own ambush with a feigned retreat, but he held his strong position. After a full day of fierce fighting that resulted in a stalemate, the Mongols retreated under darkness and attempted to hide their trail and outflank the Jin. Wan Yen Heda had retreated towards the city of Tengzhou in order to obtain supplies. Changing tracks, Subutai, identifying that the Jin were vulnerable to attrition, used a feint attack to temporarily divert the Jin forces away from their supply train, which he promptly seized with a hidden force. Rather than continually attempting to attack the vigilant Jin during their retreat, Subutai instead dispersed his army into several detachments to target supplies in the area. 3,000 men masked the Mongol dispersion and occupied the Jin's attention, while other Mongol forces slowly slipped away from the field in small numbers to hide their movements towards the Jin capital of Kaifeng, the route that Wan Yen Heda was retreating along. With part of his force harassing the Jin army's foragers, the other units marched around the flanks in a wide arc and emerged ahead of the Jin army, aiming to destroy or steal the supplies of nearby villages along the Jin's line of retreat. Ogedei Khan had been able to cross the Yellow River after the Jin army blocking him had to march south to help Wan Yan Heda. With Subutai's