After the death of Li Linfu in 753, An Lushan's rivalry with General Geshu Han and Chancellor Yang Guozhong created military tensions within the empire.

In late 755, An Lushan instigated open revolt and quickly captured Luoyang, the eastern capital, where in early 756 he proclaimed himself emperor of the new Yan dynasty.

While his generals continued his campaigns, An Lushan remained in the Luoyang palace; his health failed and he became increasingly violent and paranoid.

According to historical sources, his original name might have been Aluoshan[12] or Yaluoshan,[13][14] the latter stated in the Old Book of Tang to mean "war" in Old Turkic.

[14] It was said that An Lushan knew six non-Chinese languages, and, after he grew older, served as an interpreter in one of the military markets, which were set up by the Chinese government largely to obtain horses in exchange for silk through foreign trade.

In 732, when the general Zhang Shougui (張守珪) was governing You Prefecture (幽州, roughly modern Beijing), it was discovered that An Lushan had stolen sheep.

Zhang, seeing that he had a large body and impressed by his plea, released him and had him serve as a police officer, along with Shi, and both of them were said to be capable at catching criminals.

[13][14] By 736, An Lushan carried a general title and was serving under Zhang Shougui as an officer of the Pinglu Army (平盧軍, based in modern Chaoyang).

[30] In 744, with further praises from the powerful chancellor Li Linfu and Pei Kuan, An was, in addition to Pinglu, made the military governor of Fanyang Circuit (范陽, headquartered in modern Beijing).

His actions led to two princesses of the royal clan, who were married to Khitan and Xi leaders as part of the heqin policy, being executed in retaliation,[31] and both groups rebelled in 745, though An defeated them.

Wang, instead, led the troops himself to Xiongwu in advance of the rendezvous date and, after participating in the building project, returned with the soldiers, and submitted reports to Emperor Xuanzong that he believed An was planning treason.

At An's request, Emperor Xuanzong also gave him the governorship of Hedong Circuit (河東, headquartered in modern Taiyuan, Shanxi), in addition to Pinglu and Fanyang.

He selected some 8,000 soldiers among the surrendered Khitan, Xi, and Tongluo (同羅) tribesmen, organizing them into an elite corps known as the Yeluohe (曵落河), which meant "the brave".

He retained Gao Shang (高尚), Yan Zhuang (嚴莊), Zhang Tongru (張通儒), and Sun Xiaozhe (孫孝哲) as his strategists; and Shi Siming, An Shouzhong (安守忠), Li Guiren (李歸仁), Cai Xide (蔡希德), Niu Tingjie (牛廷玠), Xiang Runrong (向潤容), Li Tingwang (李庭望), Cui Qianyou (崔乾祐), Yin Ziqi (尹子奇), He Qiannian (何千年), Wu Lingxun (武令珣), Neng Yuanhao (能元皓), Tian Chengsi, Tian Qianzhen (田乾真), and Ashina Chengqing (阿史那承慶) as his generals.

In 752, he wanted to launch a major counterattack against the Khitan, requesting that the ethnically Tujue general Li Xianzhong (李獻忠) accompany him.

[33] Later that year, when Emperor Xuanzong, seeing that both An Lushan and An Sishun (who by this point was the military governor of Shuofang Circuit (朔方, headquartered in modern Yinchuan, Ningxia)) had poor relations with Geshu Han, the military governor of Hexi (河西, headquartered in modern Wuwei, Gansu) and Longxi (隴西, headquartered in modern Haidong prefecture, Qinghai) Circuits, and wanted to improve relations between these three key border troop commanders, he summoned all three to the capital and had the powerful eunuch Gao Lishi host a feast for the three of them, trying to get them to resolve their unpleasantries.

After that, Emperor Xuanzong refused to believe any suggestions that An was plotting rebellion despite Li Heng agreeing with Yang's assessment on this issue.

Yang then attacked some of An's staff and associates, including having the mayor of Jingzhao arrest An's friend Li Chao (李超) and others, and executing them secretly.

[34] In winter 755, An launched his rebellion on 16 December,[36] claiming he had received a secret edict from Emperor Xuanzong to advance on Chang'an to remove Yang.

The imperial officials were all apprehensive, because An had the strongest troops of the realm at the time, except for Yang, who believed that An could be suppressed easily.

Emperor Xuanzong commissioned the general Feng Changqing as military governor of Fanyang and Pinglu, intending to have him replace An after An's rebellion was defeated.

Some Tang officials north of the Yellow River resisted An Lushan under the leadership of Yan Zhenqing, the governor of Pingyuan Commandery (平原, roughly modern Dezhou, Shandong).

[34] On Lunar New Year's day, 756 (5 February[1]), An Lushan declared himself Emperor at Luoyang, establishing a new state of Yan, making Zhang Tongru and the surrendered Tang official Daxi Xun (達奚珣) his chancellors.

[14] Meanwhile, Yan Zhenqing's cousin Yan Gaoqing (顏杲卿), who initially submitted to An, rose against An at Changshan Commandery (常山, roughly modern Baoding, Hebei) but was quickly defeated and delivered to An in Luoyang; An executed him and sent An Qingxu to make an initial attack against Tong Pass, and Geshu Han repelled the attack.

[38] By this time, the Tang generals Guo Ziyi and Li Guangbi had fought their way into Emperor An's territory north of the Yellow River, cutting off the communication between Luoyang and Fanyang, causing much fear in An's troops.

An considered withdrawing north of the Yellow River to secure the territory, but meanwhile, suspicions had begun to rise between Yang Guozhong and Geshu, each believing that the other had designs on himself.

Yang therefore persuaded Emperor Xuanzong to order Geshu to attack the Yan general Cui Qianyou, who was then stationed at Shan Commandery.

[38] When Yan forces captured Tong Pass, Emperor Xuanzong and Yang, in panic, abandoned Chang'an and fled toward Shu Commandery (蜀郡, roughly modern Chengdu, Sichuan).

Hearing news of Chang'an's fall, Guo and Li Guangbi withdrew to Lingwu, allowing Shi to again pacify the region north of the Yellow River and east of the Taihang Mountains with exception of pockets held by Yan Zhenqing and other Tang officials under his command.

His sheer weight once crushed to death a horse[41] and he needed three servants to help him to put on and take off his clothes when he visited Huaqing Pool.