al-Din II. The Mongol forces sent against him in 1227 were defeated at Dameghan. Another army that marched against Jalal al-Din scored a pyrrhic victory in the vicinity of Isfahan but was unable to follow up that success. With Ögedei's consent to launch a campaign, Chormaqan qorchi left Bukhara at the head of 30,000 to 50,000 Mongol soldiers. He occupied Persia and Khorasan, two long-standing bases of Khwarazmian support. Crossing the Amu Darya River in 1230 and entering Khorasan without encountering any opposition, Chormaqan passed through quickly. He left a sizable contingent behind under the command of Dayir Baghatur, who had further instructions to invade western Afghanistan. Chormaqan and the majority of his army then entered Tabaristan (modern-day Mazandaran), a region between the Caspian Sea and Alborz mountains, in the autumn of 1230, thus avoiding the mountainous area to the south, which was controlled by the Nizari Ismailis (the Assassins). Upon reaching the city of Rey, Chormaqan made his winter camp there and dispatched his armies to pacify the rest of northern Persia. In 1231, he led his army southward and quickly captured the cities of Qum and Hamadan. From there, he sent armies into the regions of Fars and Kirman, whose rulers quickly submitted, preferring to pay tribute to Mongol overlords rather than having their states ravaged. Meanwhile, further east, Dayir Baghatur steadily achieved his goals in capturing Kabul, Ghazni, and Zabulistan. With the Mongols already in control of Persia, Jalal al-Din was isolated in Transcaucasia where he was banished. Thus all of Persia was added to the Mongol Empire. The fall of the Jin dynasty At the end of 1230, responding to the Jin's unexpected defeat of Doqolqu cherbi (Mongol general), the Khagan went south to Shanxi province with Tolui, clearing the area of the Jin forces and taking the city of Fengxiang. After passing the summer in the north, they again campaigned against the Jin in Henan, cutting through territory of South China to assault the Jin's rear. By 1232 the Jin Emperor was besieged in his capital of Kaifeng. Ögedei soon departed, leaving the final conquest to his generals. After taking several cities, the Mongols, with the belated assistance of the Song dynasty, destroyed the Jin with the fall of Caizhou in February 1234. However, a viceroy of the Song murdered a Mongol ambassador, and the Song armies recaptured the former imperial capitals of Kaifeng, Luoyang,