Just when the war in the Central Plains entered the white-hot stage, the Turkic Jieli Khan had quickly swept away the dissidents and set his sights on the Central Plains with great ambitions.

Princess Yicheng's cousin Yang Shanjing was hiding from the war in the Turks, and Wang Shichong sent a messenger Wang Wensu to the Turks to ask for help, Wang Wensu found Yang Shanjing and gave him Yang Shanjing a lot of money, and Yang Shanjing agreed to Wang Wensu's request.

Yang Shanjing persuaded Jieli Khan: "In the past, Qimin Khan was persecuted by his brothers, and after escaping, he defected to the Sui Dynasty, and it was all thanks to the power of Emperor Wen that he had the Turkic territorial monarchy, and future generations could not enjoy it. Now that the emperor of Tang is not a descendant of Emperor Wen of Sui, you should appoint Yang Zhengdao as emperor and destroy Tang to repay the kindness of Emperor Wen in the past. ”

Jieli Khan already had this intention, so he deeply agreed with Yang Shanjing's words and promised to lead a large army south in the near future.

Because Li Yuan had not yet pacified the Central Plains, he treated the Turks very generously, while Jieli Khan was excessively demanding and arrogant in his words, so he also knew that a war between the two sides was inevitable, so he made some countermeasures to this.

In March, the hussar general Ke Zhu Hun Dingyuan played: "Li Zhongwen, the governor of Shizhou, colluded with the Turks and agreed to prepare to guide the Turkic cavalry to drive directly to Chang'an when Tang and Zheng were at war. ”

On March 13, Li Yuan ordered Li Jiancheng to guard Puhan as a precaution, and then sent Tang Jian, the secretary of the Ministry of Rites, to pacify Shizhou, temporarily abolish the Shizhou Governor's Office, and urgently summon Li Zhongwen to the court.

Whether Li Zhongwen colluded with the Turks or not is just Zhu Hun's one-sided statement, and the evidence is not sufficient, but at this sensitive moment, Li Yuan would rather believe that he has it than have no surname, of course, more importantly, Li Zhongwen has no backer in the court, so that until he dies, no one asks for mercy for him.

Soon after Li Zhongwen was killed, the Jihu Liu Cheng tribe in Shizhou rebelled with the tribe, Liu Cheng was the younger brother of Liu Miao Wang, and he was very dissatisfied with the killing of his nephew Liu Jizhen, so after grasping the power of Jihu, he ignored the dissuasion of other tribes and resolutely chose to rebel against the Tang Dynasty.

On March 23, Li Yuan issued an edict ordering the crown prince Li Jiancheng to lead all the troops and horses to defeat Jihu.

After Li Jiancheng received the edict, he immediately set out from Pusaka, and soon defeated Liu Cheng and captured more than 1,000 Jihu.

After that, Li Jiancheng released dozens of Jihu chieftains and chieftains, conferred official titles on them, and asked them to return to the tribe and recruit their comrades, and Liu Cheng also surrendered.

Li Jiancheng pretended to add prefectures and counties to build cities, ordered the surrender of Jihu to be over 20 years old to gather, and then sent troops to surround and kill all of them, killing a total of more than 6,000 people, Liu Cheng found that the situation was not right, and fled to Liang Shidu.

On the second day of April, Zhang Changxun, the governor of Tang Fengzhou, returned to the DPRK, and many people who were discussing political affairs at that time said that Zhang Changxun had been in Fengzhou for a long time and had been valued by the Turks, which was not conducive to the country.

When Zhang Changxun heard these discussions, he was afraid of following in the footsteps of Li Zhongwen, so he took the initiative to ask to return to the court, and Li Yuan granted his request. It happened that Li Jiancheng went on a northern expedition to Jihu, and Zhang Changxun led the troops to join Jiancheng, returned to the court, and worshiped the right general Wuhou.

When the left servant of Yizhou Xingtai shot Dou Liang and led the soldiers and horses of Ba and Shu to join forces with Li Shimin to attack Wang Shichong, Li Yuan appointed Zhang Changxun as the right servant of Yizhou Xingtai, and the situation was immediately turned into safety.

On 16 May, thousands of Turkic troops invaded Fenyin County. On the 24th, the Turkic troops invaded Shizhou in ten thousand horses, and the newly appointed Shizhou Assassin Wang Ji repelled the invading Turkic soldiers.

These were the leading forces of the Turks.

Li Yuan was very reluctant to confront the Turks at this time, so he sent Li Xiaogong's younger brother, Li Gui, the Duke of Hanyang, to bribe Jieli Khan with heavy gold cloth, but when they met, Jieli wanted Li Gui to bow down to him, Li Gui did not obey, Jieli Khan was furious, so without saying a word, Li Gui detained Li Gui.

At the beginning, when Chu Luo Khan and Liu Wu echoed inside and outside and invaded the annexed states, Li Yuan sent Taichang Qing Zheng Yuan to Xiao Yi to bring good fortune, but Chu Luo did not hear it. Soon after, Chu Luo fell ill and died, and the Turks suspected that he had been poisoned by Zheng Yuan, so they detained Zheng Yuan and prevented him from returning to China.

Therefore, Li Gui's detention is the second time that the Turks have detained the envoy of the Tang Dynasty, Li Yuan is very angry about this, and he also detains the Turkic envoy, but there is no possibility of reconciliation between the two sides.

In June, Jieli Khan personally led an army of 200,000 to Yanmen Pass, intending to pull out the thorn in the flesh first. Moreover, the guard of Yanmen Pass is now just a small Daizhou (Yanmen County) assassin Shi Zhou'an, in Jieli's opinion, it is really not a cause for concern.

However, Jieli Khan's 200,000 troops attacked Yanmen Pass for more than a month and suffered heavy losses, but Yanmen Pass was still firmly in the hands of Zhou An.

On the city wall of Yanmen Pass, there are many medium-sized stone throwing machines, which were designed by craftsmen in Li Yin's early years, and Li gave the Turks great casualties in the rest of the month, and in addition to the stone throwing machine, there are many other city defense equipment on Yanmen Pass.

Coupled with the danger of Yanmen Pass itself, as well as the abundance of materials, although Jieli Khan had an army of 200,000, it was extremely difficult to capture it.

After fighting hard for half a month without gaining anything, Jieli Khan finally withdrew from Yanmen Pass and moved to other places.

Originally, Zhou An, who was not well-known, was soon famous all over the world after this battle, and many generals around Li Yin used to think that Li Yin entrusted Yanmen Pass to Zhou An, just to be close to Zhou An, until then it suddenly understood that the somewhat taciturn person also had good military talent.

After Jieli Khan left Yanmen Pass with soldiers and horses, he went south to invade the state, but found that the huge state was merged, but there were not a few people to see, and there were very few things to loot.

Jieli then continued to go south with a lot of popularity, but he was blocked by the Sparrow Mouse Valley and could not advance for a while. Jieli Khan went south with great ambitions, but he ran into walls everywhere and felt very depressed.

……

In September, the secret agent of the Tiger Prison Pass reported: "Because our army was grazing horses north of the Yellow River, Dou Jiande knew that our army had run out of forage and was suspected of preparing to attack the Tiger Prison." ”

On the third day of the first month, Li Yin crossed the Yellow River to the north, forced into Guangwu from the south, reconnoitred the enemy, took the opportunity to leave more than 1,000 horses, grazing cattle by the Yellow River to lure Dou Jiande, and returned to the Tiger Prison that night.

On the fourth day of the first month, Dou Jiande really poured out of the nest, from Banzhu out of the Niukou battle array, north of the Yellow River, west of Bishui, south of Queshan, continuous twenty miles, drumming forward.