In 1235, the year following the immolation of Ninkiassu, the Mongols placed half a million men in the field for the purpose of destroying the Sung power, and Ogotai divided them into three armies, which were to attack Litsong's kingdom from as many sides. The Mongol ruler intrusted the most difficult task to his son Kutan, who invaded the inaccessible and vast province of Szchuen, at the head of one of these armies. Notwithstanding its natural capacity for offering an advantageous defense, the Chinese turned their opportunities to poor account, and the Mongols succeeded in capturing all its frontier fortresses, with little or no resistance. The shortcomings of the defense can be inferred from the circumstances of the Chinese annalists making special mention of one governor having had the courage to die at his post. For some reason not clearly stated the Mongols did not attempt to retain possession of Szchuen on this occasion. They withdrew when they were in successful occupation of the northern half of the province, and when it seemed as if the other lay at their mercy. In the two dual provinces of Kiangnan and Houkwang, the other Mongol armies met with considerable success, which was dimmed, however, by the death of Kuchu, the son and proclaimed heir of Ogotai. This event, entailing no inconsiderable doubt and long-continued disputes as to the succession, was followed by the withdrawal of the Mongol forces from Sung territory, and during the last six years of his life Ogotai abstained from war, and gave himself up to the indulgence of his gluttony. He built a great palace at Karakoram, where his ancestors had been content to live in a tent, and he intrusted the government of the old Kin dominions to Yeliu Chutsai, who acquired great popularity among the Chinese for his clemency and regard for their customs. Yeliu Chutsai adopted the Chinese mode of taxation, and when Ogotai's widow, Turakina, who acted as regent after her husband's death, ordered him to alter his system and to farm out the revenues, he sent in his resignation, and, it is said, died of grief shortly afterward. Ogotai was one of the most humane and amiable of all the Mongol rulers, and Yeliu Chutsai imitated his master. Of the latter the Chinese contemporary writers said "he was distinguished by a rare disinterestedness. Of a very broad intellect, he was able, without injustice and without wronging a single person, to amass vast treasures (D'Ohsson says only of books, maps, and pictures), and to enrich his family, but all his care and labors had for their sole object the advantage and glory of his masters. Wise and calculating in his plans, he did little of which he had any reason to repent."