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Taizong (926–947)

Yelü Deguang, posthumously Emperor Taizong of Liao, was the second son of Shulü Ping and not the first in line for the Khitan throne. His elder brother, the 26-year old heir apparent Yelü Bei, was disliked by the conservative Khitan elites for his intellectual pursuits. As a polymath, Yelü Bei was skilled in painting, writing in both Khitan and Chinese languages, and possessed a large personal library. He also had a taste for Chinese culture, music, medicine, and prognostication. Chinese-style primogeniture was also not a custom among the Khitans, who had elected their leader since the time of the Dahe Confederation, which was why Abaoji had them swear allegiance to Yelü Bei when he announced him as heir apparent. Bei's mother, Shulü Ping, who was exceptionally powerful in her own right, commanding thousands of horsemen and leading troops on campaign, took control of all military and civil affairs as regent, after having cut off her right hand to be buried with her husband. Shulü Ping herself disproved of her first son as heir due to his Chinese leanings and used all her influence to have Bei set aside for his younger brother, Deguang, who had participated in the 922–923 and 924–925 campaigns. Toward the end of 927, Bei approached his mother and formally withdrew his claim. Deguang succeeded the throne.

"The ruler who has received the Mandate of Heaven should be attentive to Heaven and respectful to the great spirits. To those of greatest merit I should offer my veneration. Which among them ranks first?" All present replied that it should be the Buddha. Abaoji responded: "Buddhism is not a Chinese teaching." Then Prince Bei spoke: "Confucius is the great sage, revered for myriad generations. He should rank first." Abaoji was delighted. Thereupon he ordered that a Confucian temple be constructed and decreed that the heir himself should conduct the spring and autumn ritual offerings.

Bei was still ruler of the Dongdan Kingdom in former Balhae, given to him by his father after participating in its conquest. Taizong, who still regarded him as a threat, ordered in 929 that the capital of Dongdan and all its inhabitants be moved to the Eastern Capital (Dongjing). Dongdan lost its semi-autonomous status. In 930, Bei fled by sea to the Later Tang court and was received by Li Siyuan as an honored guest. In 937, he was killed by Shi Jingtang, who overthrew Later Tang and ruled Later Jin (Five Dynasties) as a puppet of the Khitans.

In 929, the Khongirad rebelled. In the same year, Taizong sent his younger brother, Yelü Lihu, to attack the Later Tang at Datong. In 933, Taizong led a campaign against some Tangut tribes. The most important expansion of Khitan territory during this period, however, came from political instability in the south. In 933, the Later Tang emperor died. His son, Li Conghou, lasted only five months before his adoptive brother, Li Congke, killed him. Li Congke ordered a powerful governor, Shi Jingtang, to be transferred for closer supervision by the court, leading to his rebellion. Hard pressed by Li Congke, Shi Jingtang sought aid from the Khitans. Taizong led a 50,000 strong cavalry force to his aid and defeated the Later Tang army near Taiyuan. On 28 November 936, Shi Jingtang was invested as emperor of Later Jin by the Khitans. In 938, the puppet emperor of Later Jin transferred the Sixteen Prefectures over to the Khitans, granting them access to the strategic fortifications of northern China and the Central Plains. A new "Southern Capital" (Nanjing) was constructed at modern Beijing. Shi Jingtang behaved as a vassal and even allowed Khitan envoys to cross his territory to contact Southern Tang, his geopolitical rival.

Shi Jingtang died in 942. His nephew and successor, Shi Chonggui, came under the influence of an anti-Khitan court led by the army commander Jing Yanguang. In 943, Shi Chonggui revoked the trading privileges of the Khitans in Kaifeng and confiscated their property, sending their representative back to the Khitan court. Taizong invaded in the following year but suffered a defeat in 945, having to escape the battle on a camel. However, with persistence, the Khitans wore down the Jin forces, and in 946, the Jin commander in chief, Du Chongwei, surrendered. In early 947, Taizong entered Kaifeng unopposed. The Jin emperor and his family were exiled to the Supreme Capital. The Jin army was disarmed and disbanded, their horses confiscated. With this great victory, Taizong formally adopted a dynastic name, the "Great Liao". With the conquest of Later Jin, the Liao acquired the Jade Seal of State Transmission (chuanguo yuxi). Ideologically, the Liao therefore regarded itself as the legitimate successor of the Later Jin, and the ruler of China. It hence chose the Water element, the element that follows the Metal element, the dynastic element of the Later Jin, according to the sequence of creation of the Five Elements (wuxing). It also chose the Water element's corresponding color black as its dynastic color.

His victory did not last. Having brought inadequate supplies, the Khitans wantonly looted the city and plundered the countryside provisions, and imposed harsh levies on the local populace, causing them to become resentful and attack them. Rather than stay and govern the conquered city, the Khitans decided to ship everything of value, from Jin officials and palace women to maps and music instruments, back to the Supreme Capital. Taizong also faced another threat from Taiyuan, where Liu Zhiyuan announced a new Later Han (Five Dynasties) dynasty. The occupation of Kaifeng lasted three months before Taizong withdrew. Shortly before reaching Liao territory, Taizong suddenly fell ill and died near modern-day Shijiazhuang at the age of 45 on 18 May 947.