The subsequent career of the Mongol chief was one of striking vicissitudes. His power grew until the question of the dominion of the steppes rested upon a great battle between the Mongols and the powerful tribe of the Keraits. The latter won the victory, the Mongols were slain in thousands, and the power which Temujin had gained by years of effort was in a day overthrown. Nothing remained to him but a small band of followers, whose only strength lay in their fidelity and discipline. Yet a man of the military ability of Temujin could not long remain at so low an ebb of fortune. In a brief time he had surprised and subdued the Keraits, and next met in battle the powerful confederacy of the Naimans, whom he defeated in a stubborn and long-contested battle. This victory made him the unquestioned lord of the steppes, over all whose inhabitants the Mongols had become supreme. And now Temujin resolved to indicate his power by some title worthy of the great position he had gained. All the Mongol chiefs were summoned to the grand council or Kuriltai of the tribe, and around the national ensign, composed of nine white yak-tails, planted in the centre of the camp, the warriors gathered to hear the opinion of their chief. It was proclaimed to them that Temujin was not content with the title of Gur Khan, to which its former bearers had not given dignity, but would assume the title of Genghis Khan (Very Mighty Khan). It may be said here that there are almost as many spellings of this name as there are historians of the deeds of him that bore it. Genghis made princes of his two principal generals, rewarded all other brave officers, and in every available way cemented to his fortunes the Mongol chiefs. He was now about forty-five years of age, yet, instead of being at the end, he was but little beyond the beginning of his career. The Kins, who had conquered Northern China, and whose ruler bore the proud title of emperor, were the next to feel the power of his arms. The dominions of the king of Hia, a vassal of the Kin emperor, were invaded and his power overthrown. Genghis married his daughter, made an alliance with him, and in 1210 invaded the territory so long held by the Kins. The Great Wall, which had so often proved useless as a barrier of defence, failed to check the march of the great Mongol host, the chief who should have defended it being bribed to desert his charge. Through the opening thus offered the Mongols poured into the territory of the Kins, defeated them in every engagement in the field, overran the rich provinces held by them, and obtained a vast wealth in plunder. Yet the war was now waged against a settled and populous state, with strong walled cities and other fortified places, instead of against the scattered clans of the steppes, and, despite the many victories of the invading horde, it took twenty years of constant fighting to crush the Tartar emperor of Northern China.