As in duty bound the Koryŭ forces went north and engaged the invaders at P‘yŭng-yang. At first the latter were successful and a thousand Koryŭ troops were trampled under the hoofs of the enemy’s horses; but in the end the “Red Heads” were defeated and, retreating northwards, were hotly pursued as far as Ham-jŭng. There they were reinforced and attempted to make a new stand; but the Koryŭ troops, drunk with success, attacked them with such abandon that they were obliged to build a palisade within which they intrenched themselves. The Koryŭ generals surrounded this stockade and, by a simultaneous assault of horse and foot, broke through the barrier and put the occupants, numbering 20,000, to the sword. The leader, Whang Chi-sŭn was taken alive. A remnant fled to the Yŭn-ju River where the ice broke beneath them and 2,000 perished. The few survivors made a desperate stand on a hill but were starved out and compelled to continue their flight, in which hundreds more were cut down along the road; and at last, out of 40,000 men who had come across the Yalu, just three hundred recrossed it and were safe. Hardly had this happened when seventy boat-loads of these same “Red Heads” arrived at P‘yŭng-ju and soon after a hundred boat-loads more disembarked at An-ak and scoured the surrounding country. They were, however, soon put to flight by Gen. Yi Pang-sil whom the king rewarded richly for his services. It was at this time that the king first received an envoy from Chang Sa-sŭng, a pretender to the Mongol throne. The king made the first move toward breaking away from the Mongol yoke by sending an envoy in return. The Koryŭ court evidently was in great doubt as to just how matters were going to turn out in the struggle that was under way in China. By favoring these advances on the part of a Mongol, whether of the imperial family or not, it is probable that the king lost the good-will of the Mings who, as we shall see, looked with satisfaction upon the overthrow of Koryŭ and the founding of the present dynasty.