During Jin Li Cunxu decided to lead the army to relieve Lu Prefecture himself, and as he advanced there, he caught the Later Liang army, which was not expecting him to be able to come so quickly, by surprise. He had Li Siyuan lead the assault on the northeast side, and Zhou Dewei lead the assault on the northwest side. The Later Liang army surrounding the city collapsed, and the siege was lifted. In 912, Li Cunxu launched a major campaign, intending to destroy the
Yan state ruled by
Liu Shouguang, with Zhou in command of the overall operations. As part of the campaign, Li Siyuan was in charge of attacking Ying Prefecture (瀛州, in modern
Cangzhou,
Hebei), and he was successful in getting its prefect, Zhao Jing (趙敬), to surrender. Subsequently, when Liu sent his major general
Yuan Xingqin to his northern borders with the
Khitan Empire to await potential aid from Khitan's
Emperor Taizu, Li Cunxu sent Li Siyuan to intercept Yuan's army. Li Siyuan first attacked Wu Prefecture (武州, in modern
Zhangjiakou,
Hebei), and its prefect Gao Xinggui (高行珪) surrendered. Yuan then attacked Wu Prefecture, and when Li Siyuan came to its aid, Yuan tried to withdraw, but Li Siyuan subsequently engaged him eight times and forced him into surrendering. Li Siyuan took Yuan as an adoptive son and kept Yuan under his command. (Gao Xinggui's brother
Gao Xingzhou, whom Gao Xinggui sent to seek aid from Li Siyuan, also joined Li Siyuan's army and subsequently often commanded Li Siyuan's guards along with Li Siyuan's adoptive son
Li Congke – the son of Li Siyuan's concubine Lady Wei.) Jin forces were subsequently able to destroy Yan and add its territory to Jin. (In 915, when Li Cunxu heard of Yuan's ferocity in battle, he requested that Li Siyuan send Yuan to serve under his own personal army, and Li Siyuan, unwilling to resist the order, reluctantly sent Yuan to Li Cunxu. Li Cunxu also wanted Gao Xingzhou and tried to entice Gao with promotion offers, but Gao declined to leave Li Siyuan's command.) In 916, when the Later Liang major general
Liu Xun tried to attack Wei Prefecture (魏州, in modern
Handan,
Hebei), which had recently surrendered to Jin – an attack that Li Cunxu anticipated and therefore reacted to immediately – Li Siyuan and his adoptive brother
Li Cunshen served as main commanders under Li Cunxu. In the subsequent battle, the Jin army crushed the Later Liang army, ending Liu's hopes of defeating Li Cunxu there. When the Later Liang military governor of Zhaode Circuit (昭德, headquartered in modern Handan) subsequently abandoned the circuit in light of Liu's defeat, Li Cunxu merged Zhaode's three prefectures, which had previously belonged to Tianxiong Circuit (天雄, headquartered at Wei) back into Tianxiong, and made Li Siyuan the prefect of Zhaode's former capital Xiang Prefecture (相州). When Jin forces subsequently approached Cang Prefecture (滄州, in modern Cangzhou), Later Liang's military governor of Shunhua Circuit (順化, headquartered at Cang),
Dai Siyuan, abandoned it and fled back to Later Liang territory. Dai's officer Mao Zhang (毛璋) surrendered Cang to Jin. Li Cunxu sent Li Siyuan to pacify the region, and Li Siyuan subsequently sent Mao away to pay homage to Li Cunxu. Li Siyuan was subsequently made the military governor of Anguo Circuit (安國, headquartered in modern Xingtai). It was there where one of his officers,
An Chonghui, became a key trusted staffer. In fall 918, Li Cunxu planned to launch a major attack on Later Liang, and he gathered troops directly under his command at Wei. Zhou, Li Cunshen, and Li Siyuan all led their own troops to rendezvous with him there as well, along with troops sent by Wang Chuzhi. He crossed the
Yellow River into Later Liang territory, with the intent of destroying Later Liang. Subsequently, the joint Jin forces encountered the Later Liang forces under
He Gui at Huliu Slope (胡柳陂, in modern
Heze,
Shandong). The battle was initially a major Jin defeat, with Zhou being killed in the battle. In the confusion of the battle, Li Siyuan believed that Li Cunxu had already retreated north of the Yellow River, and therefore retreated. Li Cunxu, however, was subsequently able to turn the battle around and defeat He Gui's Later Liang forces, causing the battle to be an overall stalemate in which both sides lost over two thirds of their armies, before withdrawing back north. When Li Siyuan rendezvoused with him, Li Cunxu was displeased, believing that Li Siyuan had thought that he died and was abandoning the battle. However, as Li Congke, who got separated from Li Siyuan during the battle and ended up fighting under Li Cunxu during the second stage of the battle, had great contributions during it, Li Cunxu did not punish Li Siyuan, although he did not treat Li Siyuan with as great respect subsequently. In spring 922, in light of a Khitan incursion, Li Cunxu made Li Cunshen the military governor of Lulong (aka You Prefecture), to defend against further Khitan attack. Li Siyuan was made the military governor of Henghai Circuit (previously known as Shunhua when under Later Liang rule), which Li Cunshen had been the military governor of, but remained with Li Cunxu's army.
During Later Tang During the destruction of Later Liang In summer 923, Li Cunxu, then at Wei Prefecture, declared himself the emperor of a continuation of Tang — historically known as
Later Tang. However, at the same time as his declaration, the Later Tang state was facing several serious threats that caused its subjects to be distressed about its prospects — the Khitan Empire was continuing to harass Lulong Circuit; Later Liang had just recently seized Wei Prefecture (衛州, in modern Puyang, different than the Wei Prefecture referred to above); and Zhaoyi Circuit, previously governed by Li Sizhao but under the control of his son
Li Jitao after his battlefield death during the Zhao campaign, had just rebelled against Later Tang and pledged allegiance to Later Liang. At this juncture, though, an officer of Later Liang's Tianping Circuit (天平, headquartered in modern
Tai'an,
Shandong), Lu Shunmi (盧順密), defected to Later Tang, and revealed to Li Cunxu that Dai Siyuan, who was the military governor of Tianping, had left two unpopular officers, Liu Suiyan (劉遂嚴) and Yan Yong (燕顒), in defense of Tianping's capital Yun Prefecture (鄆州), and that a surprise attack on Yun could cause it to fall. When Li Cunxu consulted Li Siyuan, Li Siyuan, who had long wanted to have a specular achievement since the Battle of Huliu Slope, advocated carrying out this attack and volunteered to command his own troops. Li Cunxu agreed, and Li Siyuan thereafter led 5,000 elite soldiers and launched a surprise attack across the Yellow River, catching Liu and Yan unaware. When he quickly entered the city, Liu and Yan fled to the Later Liang capital
Daliang. Li Cunxu thereafter commissioned Li Siyuan as the military governor of Tianping. Subsequently, the Later Liang emperor
Zhu Youzhen (Zhu Quanzhong's son) replaced Dai with
Wang Yanzhang, who tried to cut off the communications between Yun and the rest of Later Tang territory north of the Yellow River by capturing the fords at Desheng and Yangliu (楊劉, in modern
Liaocheng,
Shandong). He captured Desheng quickly, but Yangliu's defenses held under the defense of Li Zhou (李周), and Li Cunxu was subsequently able to lift the siege on Yangliu, allowing Yun to remain in contact with Later Tang proper. In summer 924, the Anyi Circuit (安義, i.e., formerly Zhaoyi) officer Yang Li (楊立), who had previously been trusted by Li Jitao, whom Li Cunxu had executed after his conquest of Later Liang, mutinied and seized control of Anyi's capital Lu Prefecture. Li Cunxu sent Li Siyuan to command the forces against Yang, with Yuan Xingqin — now with the imperially-bestowed name of Li Sharing — and Zhang Tingyun (張廷蘊) serving as his deputies. Zhang quickly advanced to Luo and entered it, capturing Yang and his coconspirators, before Li Siyuan and Li Shaorong could arrive. (Yang and his coconspirators were subsequently delivered to then-Later Tang capital
Luoyang and executed.) After this campaign, Li Siyuan was made the military governor of Xuanwu Circuit and the commander of the Han and non-Han cavalry and infantry forces, replacing the recently deceased Li Cunshen.
During the collapse of Li Cunxu's reign Soon after Former Shu's fall, however, Li Cunxu and his wife
Empress Liu came to suspect Guo Chongtao of hoarding wealth and planning to occupy Former Shu's territory to rebel himself. Empress Liu wanted to order Guo's death, and, after Li Cunxu initially refused to issue such an edict, issued her own edict to Li JIji and ordered Guo's death. Li Jiji carried the order out, leading to much shock and dissension among the imperial troops. Li Cunxu's subsequent execution of another major general,
Li Jilin, only added to such dissent. Kang Yanxiao subsequently rebelled, and while his rebellion was quickly suppressed, the soldiers' dissensions continued, particularly because at that time, the Luoyang region was stricken with famine, leading to many rumors. Li Siyuan was also the subject of many rumors, leading to Li Cunxu's sending his close associate
Zhu Shouyin to meet with and observe Li Siyuan. Zhu secretly informed Li Siyuan of this and stated, "Your achievements, Lord Chancellor, make your Lord comprehensive about you. You should consider trying to return to your fief to avoid disaster." Li Siyuan responded, "My heart does not sin against heaven or earth. If disasters come, I cannot avoid it. It will be my lot." It was said that several times Li Cunxu came to believe the rumors about Li Siyuan, but Li Cunxu's director of palace affairs,
Li Shaohong protected Li Siyuan such that no disaster came to Li Siyuan. At that time, Li Cunxu was faced with several mutinies north of the Yellow River, the chief of which was at Xingtang, where the soldiers had forced the officer Zhao Zaili (趙在禮) into leading them in mutiny. Li Cunxu initially sent Li Shaorong to try to quell the rebellion, but Li Shaorong's siege of Xingtang was fruitless. The key officials, including
Zhang Quanyi and Li Shaohong, all recommended that he send Li Siyuan, and despite his hesitations, he put Li Siyuan in command of the imperial guards and sent him against the Xingtang rebels. Li Siyuan subsequently arrived at Xingtang and put it under siege, but that night, the officer Zhang Pobai (張破敗) led a mutiny and took Li Siyuan and his deputy Huo Yanwei — now with the imperially-bestowed name of Li Shaozhen — hostage, forcing them to join the Xingtang rebels. After some initial confusions in which the Xingtang rebels attacked and killed Zhang, the Xingtang rebels welcomed Li Siyuan and Li Shaozhen into the city, but subsequently allowed them to leave to regather their troops, after Li Siyuan made assurances to ally with them. By this point, Li Shaorong, believing that Li Siyuan was rebelling against Li Cunxu, withdrew from the Xingtang vicinity and submitted reports to Li Cunxu that Li Siyuan had rebelled. Li Siyuan, with some Chengde troops who initially fled the scene having rejoined him, considered his options. He initially wanted to return to Chengde and then submitting a petition begging forgiveness for being unable to properly rein in his troops, but Li Shaozhen and An Chonghui pointed out that he would then be vulnerable to accusations of occupying the land for his own benefit. They, instead, recommended heading toward Luoyang to try to defend himself against Li Shaorong's accusations. On the way, he sent a number of messengers to Li Cunxu, hoping to explain himself, but these messengers were all intercepted and killed by Li Shaorong. Li Cunxu's attempt to verify Li Siyuan's intentions by sending Li Siyuan's son Li Congshen (李從審) to Li Siyuan was also thwarted by Li Shaorong, who eventually killed Li Congshen. Under the advice of his son-in-law
Shi Jingtang, Li Siyuan changed his posture and instead prepared for battle against the imperial troops. He headed toward Daliang, as Li Cunxu also prepared to do so. When he reached Daliang first, the defender of Daliang,
Kong Xun, welcomed him in, causing Li Cunxu, then on the way, to be dejected, and Li Cunxu returned to Luoyang. Shortly after, a mutiny occurred at Luoyang as well, and Li Cunxu was killed in battle while battling the mutineers. Li Siyuan subsequently arrived at Luoyang at Zhu Shouyin's invitation. Initially, he stayed at his own mansion and ordered the soldiers to stop looting; he also gathered Li Cunxu's remains to prepare for funeral. When the officials encouraged him to take the throne, he declined, and stated to Zhu that he should continue to treat Li Cunxu's consorts
Consort Han and Consort Yin with respect, and prepare for the return of Li Jiji, suggesting that he would return to Chengde once Li Cunxu was buried and Li Jiji took the throne. However, after repeated requests by officials, he took the title of
regent. He issued orders for the imperial princes to be found. Li Shaozhen and An Chonghui, however, believing the situation to be untenable, secretly had two of Li Cunxu's younger brothers, Li Cunque (李存確) the Prince of Tong and Li Cunji (李存紀) the Prince of Ya, assassinated. By Li Siyuan's orders, Empress Liu, who fled to Taiyuan, was killed, and the soldiers also killed Li Cunxu's brothers Li Cunwo (李存渥) the Prince of Shen and Li Cunba (李存霸) the Prince of Yong. Several other imperial princes were never located, and only Li Cunxu's brother Li Cunmei (李存美) the Prince of Yong (different title than Li Cunba's) was spared on account of his illness. When Li Shaorong was captured, Li Siyuan personally questioned him, "How have I wronged you that you killed my son?" Li Shaorong stared at him and responded, "How has the deceased emperor wronged you?" Li Siyuan had him executed and his name changed back to Yuan Xingqin. With the possibilities of a rapprochement with Li Jiji gone, Li Siyuan decided to resist Li Jiji's return. He sent Shi Jingtang and Li Congke to take up defensive positions at Shan Prefecture (陝州, in modern
Sanmenxia,
Henan), and Hezhong Municipality (河中, in modern
Yuncheng,
Shanxi), respectively, to block Li Jiji's potential return. Shortly after, with his own associates abandoning him, Li Jiji committed suicide. The general
Ren Huan took over command of his army; when the army met Shi's, they submitted to Li Siyuan's rule. With Li Jiji eliminated, Li Siyuan prepared to take the throne himself. Li Shaozhen and Kong Xun, believing that Tang's heavenly mandate was over, advocated that he change the name of the state. However, Li Siyuan, citing the fact that he had long served Li Guochang, Li Keyong, and Li Cunxu, declined. Under the suggestion of
Li Qi, he took the position that he was succeeding Li Cunxu legitimately, and, after a ceremony in which he first mourned Li Cunxu, took the throne as the new emperor. ==Reign==