In medieval China, Yan'an was once called Yanzhou, a location of strategic military importance for the Chinese empire and Tanguts of the Western Xia Dynasty. It was once successfully defended by the Song Dynasty (960 to 1279) era Chinese scientist, statesman, and general Shen Kuo (1031-1095 AD). However, it was eventually taken over by the Tanguts in 1082 once Shen's defensive victories were marginalized and sacrificed by the new Chancellor Cai Que (who handed the city over to the Tanguts as terms of a peace treaty). Yan'an and the whole of Shaanxi were taken over by the Mongols in the late 1220s, only after their leader Genghis Khan had died during the siege of the Western Xia capital in 1227. The city was maintained by the successive Chinese Ming Dynasty (1368-1644), as well as the Manchu Qing Dynasty (1644-1911). After the fall of the Qing Dynasty, the city fell into the hands of the newly-created Republic of China. In December 1936, at the start of the Second United Front, Yan'an was taken over by the Chinese Communists.