Datong is located in the center of the Datong Basin in the north of Shanxi, the northeast edge of the Loess Plateau, is the barrier of the whole Jin Dynasty, the gateway of the north, the throat of the Jin Dynasty and Beijing, is the place where the soldiers of the past dynasties must fight, and is called the "key to the north".

Because Zhu Ming drove the Mongols out of the border and won the world, after Zhu Yuanzhang became emperor, in order to resist the possible counterattack invasion of the Mongols, he established many border towns along the Great Wall. After the Yongle Emperor Zhu Di moved the capital to Beijing, he set up nine towns of Liaodong, Xuanfu, Datong, Jizhou, Yansui, Ningxia, Gansu, Shanxi and Guyuan, which were known as "important towns on the nine sides" in history.

The Nine Sides were an important front for the Ming Dynasty to defend against the remnants of the Mongols, and Datong was one of the most important military towns.

Datong town at the beginning of the 26th Lingwei, the jurisdiction of the east to the Juyong Pass in Beijing, west from the Yellow River bend of the partial pass, east and west stretching more than 1,000 kilometers, north and south also have hundreds of kilometers, its scope is large, it is the first of the nine sides. Rear guard fourteen, there are Datong avant-garde, guard, left guard, Yanghe, Tiancheng, Weiyuan, Pinglu, Yunchuan, Yulin, Zhenlu, Gaoshan, Xuande, Dongsheng.

When Yongle set up Datong Town in the seventh year, he set up a town guard chief officer and was the supreme commander of the town. Chenghua set up a governor in seven years, Zhengde set up a general system in eight years, governed thirteen guards, eight hundred and twenty-three forts, three hundred and seven piers, and the garrison reached more than 130,000 at most.

At the end of Wanli, Liaodong Jiannu raised troops and committed the Ming Dynasty. Shortly thereafter, the people of Shanxi changed, the thieves swarmed, the Central Plains was in turmoil, the Ming court had to draw troops from the towns on the nine sides to resist the captives and rebellion, and in the Chongzhen years, there were few hundred thousand elite border troops left in the towns of the nine sides. In the recent Battle of Songshan, the only elite of the border army of the Ming Dynasty also lost most of it, and the Datong town soldiers were almost lost.

Clear-sighted people like Hong Chengchou know that the situation in Liaodong has not changed greatly because of Cao Yue's surprise attack on Shengjing, and Jiannu's strength has not suffered major losses, and in a few years, they will definitely make a comeback. On the Shanxi side, the army of thieves such as Li Zicheng and Zhang Xianzhong is getting stronger and stronger. The crisis in Daming shows no signs of lifting, and the situation is still not optimistic. Adequate preparations must be made, especially with regard to armaments.

Cao Yue was able to serve as the commander-in-chief of Datong, mainly because of his heroic performance in the surprise attack on Shengjing, as well as Hong Chengchou's strong recommendation.

Hong Chengchou can be said to be one of the most discerning people in the Ming court, he knows that the situation is critical, the border army of the Ming Dynasty has been lost, if there is no new army to train, when the Jiannu or the thieves come over, the court will have no soldiers available. After the Battle of Songshan, it was the top priority to train a group of capable soldiers as soon as possible, and Hong Chengchou had already ordered Cao Bianjiao to do this in Liaodong.

When Cao Yue led the army back to Songshan in triumph, Hong Chengchou talked to him a lot. After Cao Yue escorted Chuanguo Yuxi back to Beijing, Hong Chengchou talked to Cao Bianjiao about a lot of things about the expansion of the army, recognized Cao Bianjiao and Cao Yue's ability, and felt that it would be a very good choice to let Cao Yue go to Datong. Cao Yue was capable, and Cao Wenzhao had been guarding Datong for many years, and finally strongly recommended Cao Yue to be the chief soldier of Datong.

Emperor Chongzhen, who received several secret reports from Hong Chengchou, also knew the crisis of the Ming Dynasty today, and recognized Hong Chengchou's recommendation, and tried to exclude Cao Yue, a member of the House of Representatives, to serve as the general soldier of Datong, and rewarded Cao Yue with a sword, giving Cao Yue special powers, hoping to have an elite army to train.

Cao Yue's father is a good general of the Ming Dynasty, Cao Yue's cousin Cao Bianjiao is brave and strategic, Cao Yue himself performed remarkably in this surprise attack on Shengjing, Hong Chengchou repeatedly recommended after Chen Ming's interests, and Emperor Chongzhen also made up his mind to hand over Datong to Cao Yue to guard.

Emperor Chongzhen hoped that Cao Yue could rely on his bravery and ability to defend Datong when the slaves or thieves came to attack, and at the same time train elite soldiers. Before Cao Yue arrived in Datong, he gave a secret decree to Wang Qiaonian, the governor of Shanxi, Chen Chunde, the political envoy of Shanxi, and Wei Daben, the prefect of Datong, asking them to give Cao Yue convenience and not make any difficulties.

But Emperor Chongzhen was a suspicious person, he was not worried about any ministers, especially the generals with heavy troops, for fear that they would support their own troops, so he also ordered Wang Qiaonian and Chen Chunde and others to do a lot of things in the secret decree, so that they could elbow Cao Yue.

Of course, Cao Yue didn't know anything about all this. When he rushed to Datong, he was full of pride.

At a young age, he became the commander of a hot town, and Emperor Chongzhen gave him special powers, allowing him to act cheaply many times. Cao Yue felt that this was an excellent opportunity for him to show his talents, and if he could grasp this opportunity, maybe he would be able to step onto the stage of history and become a powerful figure, and maybe he could use it to completely change history.

However, on the way to Datong, Cao Yue received information from Cao Jie, who arrived in Datong first, and his enthusiasm was extinguished a lot.

During the Chongzhen period, the towns on the nine sides not only had to resist the attacks of Jiannu and the Mongol cavalry, but also had to clear out the large and small horse thieves, bandits and bandits, and also had to deal with the thieves. Datong Town is even more, because Wang Pu threw down the army and fled alone, the original Datong Town soldiers who were transferred to Liaodong are almost gone. Today's Datong has less than 3,000 people, and most of them are old, weak, sick and disabled. What's even worse is that these less than 3,000 men and horses, military discipline is corrupt, and robbing the people often occurs, which can be said to be even more hateful than bandits.

What Cao Yue wants to take over is a mess, and one more important point is that Datong City is now very dilapidated and urgently needs to be repaired.

The geographical location of Datong determines that this is a fortress that often has to experience the baptism of war. The Mongols and Jiannu went south to attack Guannai, often attacking from Datong, and the thieves wanted to attack Beijing, and Datong was almost the only way to go. Datong was sandwiched between the Mongols, the Jiannu and the rebel armies, and because it was not far from Beijing, it was always constrained by the imperial court.

Now the forces of Jiannu and Mongolia have not been greatly damaged, but the two rebel armies of Li Zicheng and Zhang Xianzhong in the Central Plains have become the climate, and the enemy may be killed at any time. It's almost winter, and if you don't solve these problems before the cold weather, this winter, maybe there will be a disaster, and the time left for Cao Yue is not at all.

After receiving Cao Jie's letter, Cao Yue was hit a little, but soon his confidence was rekindled.

Young people are not afraid of setbacks and difficulties, as long as they have determination and confidence, no matter how big the difficulties are, they can solve them. A mess is nothing, as long as you clean it up with your heart, you will definitely be able to get rid of the rotten things, and it will be the same clear world.

One thing that made Cao Yue very happy was that when he set off from Beijing, he had 3,000 soldiers with him. The combat effectiveness of these 3,000 men and horses is far more powerful than that of the ordinary Ming army, and most of them are the subordinates of Cao Wenzhao in the past, as long as they are trained more, there is no problem with loyalty.

With 3,000 men and horses by his side, even if there is a civil uprising, or an invasion by Jiannu and Mongols, it will definitely be no problem to resist for a while. Of course, after arriving in Datong, it is most important to immediately reorganize the army, recruit new soldiers, and step up training.