After Wang Shichong defeated Li Mi, his prestige was greatly boosted, and he returned to Luoyang, where Yang Tong named him Taiwei and asked him to establish the Taiwei Mansion.

Yang Tong's subordinates said: "Your Majesty, now that Wang Shichong is full of prestige, his power is extreme, and he often has the heart of Sima Zhao, why don't you take the opportunity of his entry into the court tomorrow to design and get rid of him, and completely return to power with Your Majesty. ”

Yang Tong was already deeply dissatisfied with being a puppet emperor, but now if he didn't get rid of Wang Shichong, he was afraid that he would be killed by him in the future, so he asked people to prepare.

The next day, Wang Shichong entered the palace to thank him, Yang Tong gave a banquet, and the monarch and ministers took a happy stand. After a few days, Wang Shichong suddenly felt abdominal discomfort, ran to the toilet many times and pulled a little prostration, looked for Lang Zhong, said that he was hit by chronic poison, and he would collapse and die after three days, but fortunately, the treatment was timely, and Wang Shichong was quickly out of danger.

Afterwards, Wang Shichong thought hard for a long time, and did not know when he was poisoned, he suspected that the emperor who entered the palace a few days ago gave a banquet to someone to move his hands and feet, so since then he never went to see Yang Dong again, and let his subordinates force Yang Dong to give him clothes, Zhu Hu, Na Ma, chariots and horses, musical instruments, tiger Ben, axes, bows and arrows, bamboo mustaches and other nine kinds of utensils, commonly known as Jia Jiu Xi, the emperor's pomp.

In March 619, Yang Tong was forced to crown Wang Shichong as King Zheng and Xiangguo, commanding hundreds of officials and adding nine tins. In April of the same year, Wang Shichong accepted Yang Dong's Chan concession and officially ascended the throne as the emperor, with the country name Zheng, and killed Yang Tong in June.

At this time, Liu Wuzhou, who was gathered in Mayi in the north, with the help of the Turks, was growing his troops and horses, and intended to go south to capture Guanzhong, and then chase the ambition of the Central Plains.

Liu Wuzhou's subordinates had a general named Song Jingang, who was superior in civil and military affairs, and suggested to Liu Wuzhou: "If the king has the heart to fight for the world, I suggest that you use the power of the Turks to first capture Taiyuan, and then use Taiyuan as a base to chase the Central Plains to the south and conquer the world." ”

Liu Wuzhou felt that what Song Jingang said was very true, so he sent an envoy with a large number of gold and silver treasures and countless beauties to meet the Turkic father Khan with his son, and after receiving the promise of the Turkic troops to assist, he ordered Song Jingang to lead troops to attack Bingzhou.

The Tang Dynasty sent the governor in Bingzhou was Li Yuanji, the son of Li Yuan, the king of Qi, Li Yuanji saw that Song Jingang was coming, and the Turks helped him, so he led his troops to resist the enemy while sending people to Chang'an for help.

Li Yuan sent two people to help, but they were defeated by Song Jingang, and Li Yuanji, who was guarding in Bingzhou, was the youngest son of Li Yuan and was deeply loved by his parents, so he let him guard Li Tang's Longxing land, but his people were insidious and cunning, and he had no talent.

Liu Wuzhou successfully occupied Taiyuan, and the generals of the neighboring prefectures and counties had more old Sui Dynasty troops, and when they saw that Liu Wuzhou was powerful, they defected to Liu Wuzhou, and soon most of Shanxi was under Liu Wuzhou's rule.

For a time, the world shook, the Tang Dynasty's territory east of the Yellow River was left in the southwest corner of Jin, Li Yuan in Chang'an was shocked, issued a handwritten handwriting: "The thief army is mighty, it is really difficult to defeat them in the short term, we should give up the land east of the Yellow River, and strictly defend the land west of Hangu Pass, so as not to let the thief army break through." ”

The reason why the Tang Dynasty lost Taiyuan was because Li Yuan used troops improperly, originally his second son Li Shimin was an expert in marching and fighting, but he was afraid that his second son would threaten the status of the prince, so he hid Li Shimin in the snow and raised him with good food and drink.

Now that the land of Longxing is lost, once the thief army invades Guanzhong, Li Tang will be in danger in the world, and it is likely to turn into dust like other anti-kings.

So Li Yuan ordered Li Shimin to lead his troops to the expedition on the one hand, and asked for help from Gao Fuji in the south of the Yangtze River on the other. Gao Buer received Li Yuan's distress document and immediately ordered Yu Shinan to lead 70,000 troops and horses in Guanzhong to cross the Yangtze River north to aid Li Yuan.

As soon as Yu Shinan led the army across the Yangtze River, it attracted the attention of various grass kings, broke the tacit understanding that the Jiangbei army could not pass the river, and at the same time directly threatened the major rebel armies in Jiangbei.

Li Shimin, who was confronting Liu Wuzhou in Baibi, heard that the King of Chu in Jiangnan came to help him in the big tent, and he was very sure that this father had nothing to say to his family, especially to himself, and directly let him take over the Xuanjia Army.

Yu Shinan led the army to arrive, met Li Shimin who personally greeted him at the camp gate, and bowed down and said: "Under the command of the King of Chu, Yu Shinan, the general of the former army, has seen His Royal Highness the King of Qin, and the King of Chu confessed before coming, and the army is under the command of the King of Qin, and he is under the command of the King of Qin. ”

Li Shimin helped Yu Shinan up and said: "General, please get up, I don't know if the emperor's uncle is good?" The royal aunts can be at peace. ”

When Yu Shinan came, Gao Buer told him to see Li Shimin to perform a courtier gift, and he thought that Gao Buer was his uncle's caring junior, but when he saw Li Shimin personally come out of the camp to greet him, and personally helped himself, combined with his great military exploits, Yu Shinan had to take a look at the young prince, and said secretly: "If you have a son like this, why worry about it." ”

Hearing Li Shimin's question, he hugged his fists and said: "Back to the King of Qin, the King of Chu and the princesses are all right, the King of Chu instructed that there is no need to go back to Jiangnan, just serve under the command of the King of Qin, and ask the King of Qin to take care of it." ”

"Where is the general, you are from Uncle Huang, we are a family, quickly follow me into the account, I will take the wind and wash the dust for the general." After that, he took Yu Shinan to the big tent of the Chinese army.

Yu Shinan brought 70,000 horses, left 20,000 to Chang'an, brought 50,000 to Li Shimin, plus the previous 60,000 horses, Li Shimin's army reached 110,000, almost the same as Liu Wuzhou. However, Liu Wuzhou had 70,000 or 80,000 Turkic soldiers and horses, and it was difficult to assess the combat strength of both sides.