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Return to China and final campaign (1222–1227)

Genghis abruptly halted his Central Asian campaigns in 1221. Initially aiming to return via India, Genghis realised that the heat and humidity of the South Asian climate impeded his army's skills, while the omens were additionally unfavourable. Although the Mongols spent much of 1222 repeatedly overcoming rebellions in Khorasan, they withdrew completely from the region to avoid overextending themselves, setting their new frontier on the Amu Darya river. During his lengthy return journey, Genghis prepared a new administrative division which would govern the conquered territories, appointing darughachi (commissioners, lit. "those who press the seal") and basqaq (local officials) to manage the region back to normalcy. He also summoned and spoke with the Taoist patriarch Changchun in the Hindu Kush. The khan listened attentively to Changchun's teachings and granted his followers numerous privileges, including tax exemptions and authority over all monks throughout the empire—a grant which the Taoists later used to try to gain superiority over Buddhism.

The usual reason given for the halting of the campaign is that the Western Xia, having declined to provide auxiliaries for the 1219 invasion, had additionally disobeyed Muqali in his campaign against the remaining Jin in Shaanxi. May has disputed this, arguing that the Xia fought in concert with Muqali until his death in 1223, when, frustrated by Mongol control and sensing an opportunity with Genghis campaigning in Central Asia, they ceased fighting. In either case, Genghis initially attempted to resolve the situation diplomatically, but when the Xia elite failed to come to an agreement on the hostages they were to send to the Mongols, he lost patience.

Returning to Mongolia in early 1225, Genghis spent the year in preparation for a campaign against them. This began in the first months of 1226 with the capture of Khara-Khoto on the Xia's western border. The invasion proceeded apace. Genghis ordered that the cities of the Gansu Corridor be sacked one by one, granting clemency only to a few. Having crossed the Yellow River in autumn, the Mongols besieged present-day Lingwu, located just 30 kilometres (19 mi) south of the Xia capital Zhongxing, in November. On 4 December, Genghis decisively defeated a Xia relief army; the khan left the siege of the capital to his generals and moved southwards with Subutai to plunder and secure Jin territories.