The Mongol Alliance and the War that Followed
By the time Lizong came to the throne, the Mongols had been attacking the Jin dynasty, which held northern China, for more than a decade. In 1231 a Mongol army marched through Song territory in the Sichuan border passes to outflank the Jin, clashing with Song forces on the way.
In 1233 the Song agreed to join the Mongols against the Jin. According to the Jin histories, the last Jin emperor, Aizong, warned that once the Jin had fallen the Mongols would turn on the Song, but the Song court saw a chance to recover the north and to take revenge for the loss of Kaifeng a century earlier. Song and Mongol armies took the last Jin stronghold at Caizhou in 1234, and the Jin dynasty ended.
The Occupation of Kaifeng and Luoyang
Shi Miyuan had died in 1233, and Lizong now took charge himself, bringing respected scholar-officials back into government in what is known as the Duanping reform. In the summer of 1234 Song armies moved north and occupied the former capitals Kaifeng and Luoyang, which lay in the territory left empty by the fall of the Jin.
The venture was a disaster. The armies were short of supplies, the Mongols broke the Yellow River dykes and flooded the approaches, and the Song forces at Luoyang were attacked and driven out. The Mongols treated the advance as a breach of their agreement, and from 1235 they were at war with the Song. The fighting continued, with pauses, for more than forty years.
The Mongol War
In 1253 the Mongols conquered the Dali kingdom in present-day Yunnan, opening a route around the Song's western flank. In 1259 the Great Khan Möngke died during the siege of the Song fortress of Diaoyu in Sichuan. His brother Kublai, who was besieging Ezhou on the Yangtze, withdrew to pursue his claim to the succession. The Song chancellor Jia Sidao, who had negotiated with Kublai, presented the withdrawal at court as a great victory, and his power grew accordingly.
In his later years Lizong took less interest in government, and his court was dominated by favourites, including the families of his consorts Jia and Yan, the eunuchs Dong Songchen and Lu Yunsheng, and the chancellor Ding Daquan.