Shi Tianze defected to the Mongol Empire's forces upon their invasion of the Jin dynasty. His son Shi Gang married a Kerait woman, the Kerait were Mongolified Turkic people and considered as part of the "Mongol nation". The Yuan dynasty created a "Han Army" () out of defected Jin troops and army of defected Song troops called the "Newly Submitted Army" (). Möngke Khan commenced a military campaign against the Chinese Song dynasty in southern China. The Mongol force which invaded southern China was far greater than the force they sent to invade the Middle East in 1256. He died in 1259 without a successor. Kublai returned from fighting the Song in 1260 when he learned that his brother, Ariq Böke, was challenging his claim to the throne. Kublai convened a kurultai in the Chinese city of Kaiping that elected him Great Khan. A rival kurultai in Mongolia proclaimed Ariq Böke Great Khan, beginning a civil war. Kublai Khan depended on the cooperation of his Chinese subjects to ensure that his army received ample resources. He bolstered his popularity among his subjects by modeling his government on the bureaucracy of traditional Chinese dynasties and adopting the Chinese era name of Zhongtong. Ariq Böke was hampered by inadequate supplies and surrendered in 1264. All of the three western khanates (Golden Horde, Chagatai Khanate and Ilkhanate) became functionally autonomous, although only the Ilkhans truly recognized Kublai as Great Khan. Civil strife had permanently divided of the Mongol Empire. The conflicts between Kublai Khan and the khanates in Central Asia led by Kaidu had lasted for a few decades, until the beginning of the 14th century, when both of them had died. Hülegü, another brother of Kublai Khan, ruled his Ilkhanate and paid homage to the Great Khan but actually established an autonomous khanate, and after Ilkhan Ghazan's enthronement in 1295, Kublai's successor Emperor Chengzong sent him a seal reading "" in Chinese script to symbolize this. The four major successor khanates never came again under true one rule, and border clashes also frequently occurred among them, although Yuan dynasty's nominal supremacy was recognized by the other three after the death of Kaidu. Instability troubled the early years of Kublai Khan's reign.