On the eve of their empire’s expansion, the Mongols were part of a central and northern Asian region dominated by competing empires, many of whom the Khan had conquered by the time of his death in 1227. Genghis Khan was proclaimed supreme ruler of the Mongols in 1206, having fought against the Tartars and other tribes, such as the Naimans and Merkits. The Mongols before Khan’s leadership were a collection of undisciplined tribes, but rapidly became a vast genocidal army who fought in cavalries of up to 200,000, wielding bows, lances and javelins. Genghis Khan began his conquests by invading and conquering the well-fortified cities of the Xixia Empire, followed by a defeat of the Jin army at Zhongdu and a Mongol occupation of the region. Prior to 1206, the Jin had been engaged in a power struggle with the Southern Sung Empire, who were later subjugated by Kublai Khan, grandson of Genghis Khan.