Bela, Subutai split his forces into several detachments. A light cavalry force under Kadan was sent to chase King Bela along the Adriatic Coast, while the main army with its siege engines under Subutai and Batu attempted to pacify Hungary proper. Other Mongol forces raided outside the borders of Hungary, even reaching Austria before being repulsed in a skirmish near Wiener Neustadt. The Mongols successfully besieged several cities, including the fortified city at Oradea, the castle of St. Martin of Pannonia, and the capital Esztergom, though the latter's stone citadel held out, and not all sieges proved successful. By early 1242, Subutai was discussing plans to invade the Holy Roman Empire, when news came of the death of Ögedei Khan and a revolt by the Cumans in Russia. Carpini alleges that, over the objections of Subutai, the Mongol princes withdrew the army to Mongolia for the election of a new Great Khan. This account of events is disputed, with Rashid al-Din specifically noting that Batu and Subutai only heard of the Khan's death after they had already begun the withdrawal. However, the death of Ogedei and the turmoil immediately after it prevented the Mongols from returning to Europe for decades. Still, the devastation had been immense. Subutai had devastated the agriculture of any area that was resisting. Though some of the civilians had escaped capture or death by hiding in castles, forests, or marshes, they returned to their ruined fields only to starve. Some historians have claimed that a quarter to a half of Hungary's population may have died from the invasion. Even in 1250, eight years after the Mongols had left, Hungarian King Bela wrote to Pope Innocent IV that Hungary could not withstand another invasion and would have to surrender to the Mongols if they returned. Final years After subduing a Cuman revolt in what is now Russia, Subutai turned towards Mongolia. Subutai insisted that Batu attend the kurultai to elect the successor of Ogedei in the Mongolian heartland. Batu declined to come and Güyük was elected after three years, with Subutai's support. Güyük had no love for Batu and wanted the best of the Mongol generals to be made unavailable to Batu if the feud between them came to open war. The new Khagan placed Subutai in charge, at the age of 71, of the campaign against the Song dynasty for 1246–1247. The Papal envoy Plano Carpini