Among the four counties under the jurisdiction of Chongqing, Yongkang County is both mountainous and plain, Jinyuan County attached to the city has rootless mountainous areas, Xinjin County also has a small number of hills, and only Jiangyuan County is a flat river, which is extremely conducive to agricultural production. Therefore, although the area of Jiangyuan County is not as large as that of Yongkang and Jinyuan, the grain output is the first in Chongqing, and the Perak army has also set up several large reclamation points in its territory. Although Jiangyuan County and the occupied area of the Mongol army were separated from the Jinma River, because the Perak Army controlled the river and the width of the river was difficult to cross, the Perak Army only stationed a naval company in Jiangyuan to prevent the Mongol army from crossing the river. Jiangyuan City and the various cantonment points were under the responsibility of the second-line troops of the garrison brigade, the basic militia.

The Perak Army's deployment arrangements in Jiangyuan are reasonable. Since 1242, the Mongol army has attacked Shu several times, and the plundering of Chongqing Mansion is from the ferries near Sandushui and Guankou Village. After the Perak army gained a foothold in the plains, the Mongol rangers harassed the Perak army in their jurisdictions, and most of them smuggled across the river from the above positions or the Pujiang River, and did not cross the river from the source of the river, which was close to the foot. There is no other reason than that there are no shoals in this section of the river, and it is impossible to wade through the water even in the dry winter season. The small boats of the Mongol army here are extremely limited, and it is difficult to cross the river with a squad of twenty war horses, let alone cross the river secretly on a large scale. What's more, once it was discovered by the Thunderbolt army, it would only be sunk and fed to the king, and the Mongolian army would not dare to take this risk at all.

However, during the summer harvest, the Mongol army crossed the river from the direction of Jiangyuan City. The boats they used to cross the river were the Thunderbolt grain ships. Due to the large grain output in Jiangyuan and the lack of warehouse facilities, Li Shuang transferred grain ships to dock at the Shiyutun reclamation point five miles downstream from the city, preparing to transport the grain to Qiongzhou, Dayi and Yongkang County after the grain was harvested. Although these places are also rich in grain, because the industrial and mining industries are concentrated in these places, the number of industrial workers is extremely large, and naturally there is a huge need for a large amount of grain. Since the Mongols did not have a naval army on the Jinma River, they naturally could not seize the ships by force. In fact, these ships were dedicated to the Mongol army by a Perak army officer named Chang Yuan, who was the deputy company commander of the basic company guarding Jiangyuan City.

Jiangyuan Chang's family has always produced many celebrities, many high-ranking officials and many celebrities, and they are also quite prestigious in Shudi, especially Chang Xuan is the most famous. Chang Xuan was a native of the Eastern Jin Dynasty, and his author of "Huayang National Chronicles" is known as the ancestor of local chronicles. Before Kuoduan entered Shu in 1242, the Chang family was still very prosperous, with thousands of good fields and hundreds of servants. Due to the abundant financial resources and the fact that many family members are officials in Lin'an and various places, local officials are also extremely in awe of them, and even the prefects of Jiangyuan County and Chongqing Mansion have to come to pay their respects in person, and they are in the limelight in Chongqing Mansion for a while.

"I saw him rise up a tall building, I saw him feast guests, and I saw his building collapse." The Mongol invasion turned the prosperity of the Chang family into a thing of the past. They did not flee to other places by boat like other big clans, but held their own power in Shu, thinking that even if the Mongols occupied Shu, they would have to rely on the cultural context to maintain their rule, and cultivating and reading heirlooms was what the Chang family was best at. Unexpectedly, the Mongols did not have the concept of governing the country with literature at all, and they firmly believed that force was the truth, and burning, killing and looting was the joy of life. Chang Yuan's grandfather's stubbornness and inadequacy caused the loss of his family's population, the mansion that used to be like a city was burned down, the slaves either died or fled, and even the ancestral grave was stolen and dug up by the captain of the golden school, and he was also angry to death.

After Kuduan retired from the army, Chang Yuan's father tried to revive the family business. It was only when there was a small achievement, and the Mongolian army invaded Shu several times and plundered the Wang Dechen Department in Lizhou, and plundered the family wealth that he had worked hard to accumulate. Before Liu Heima reoccupied western Sichuan, the Chang family became no different from ordinary people, except that they still held the title deed of thousands of acres of fertile land. It's just that under the troubled times, the population is more than one, and a large area of fertile land is deserted, and there is no one to cultivate its arable land at all. The Chang family had neither the population to cultivate the land nor the ability to prevent the displaced people from living on it, so they could only allow the land to be cultivated or overgrown with weeds. It's just that the Chang family is used to the scenery, and they can't accept the fact that their family is in the middle of the road. Under the anxiety, Chang Yuan's father was ill, and he told Chang Yuan before his death that he must restore the glory of the family to comfort the spirit of the ancestors.

When the Mongols were entrenched in the source of the river, Chang Yuan and a group of displaced people hid in a swamp by the Jinma River. Because Chang Yuan was literate and understood a lot of truths, he became the leader of this group of homeless people over time. When the Perak Army arrived, he was first appointed platoon commander of the militia company, and later promoted to deputy company commander of the backbone company responsible for the defense of Jiangyuan City because of his outstanding performance. Because the Chang family is deeply rooted in Jiangyuan, and Chang Yuan is good at relationships, over time, his influence in the basic company even exceeds that of the elder and the thick company commander, and he has won the support of many people. When faced with an existential threat, his father's last words only occasionally came to his mind in the dead of night. With the stability of his life and the rise of his official position, his father's last words took root like a seed and gradually grew into a towering tree, and the desire to restore the glory of the family became stronger and stronger.

The reason why Chang Yuan wanted to take refuge with the Mongols, who had a deep hatred of the sea of blood, was because of interests, and more accurately, because he was dissatisfied with the land policy of the Perak army. Land is the foundation not only of an agrarian society, but also of an industrial society. The Perak Army's fiscal and taxation system did not rely on farmland, but on industry, mining and commerce, but still placed great emphasis on arable land. After recovering the lands of these three states (prefectures and armies), the Perak Army implemented a policy of "arable land has its own land", and the ownership of the ownerless wilderness can be recognized as long as it is cultivated for a certain number of years, and no land endowment will be collected. Although the validity of the title deed is not openly denied to the owner's wasteland, the owner of the title deed is required not to leave the cultivated land uncultivated and must cultivate it himself. This policy made the land deeds in the hands of former landlords such as Chang Yuan worthless, which naturally caused them strong dissatisfaction. Some of these people claimed to complain to the imperial court, and some chose to fight fiercely. Ouyang Xuan's attitude towards this was extremely tough, and he suppressed the different voices of the management. He will never allow land annexation under the rule of the Thunderbolt Army, and "Zhumen wine and meat stink, and there are frozen bones on the road". He could not tolerate the disparity between the rich and the poor and social injustice.

There is a saying in western Sichuan that "a dog that barks does not bite, and a dog that bites does not bark". To the Thunderbolt Army and even Ouyang Xuan, although Chang Yuan hated it so much, he did not show it, on the contrary, he treated the people more kindly and his colleagues more attentively, so that no one knew his resentment. In fact, he took advantage of the shortcomings and omissions in the administration of the Perak Army to secretly incite discontent, and over time he gathered around him a group of people who were dissatisfied with the Perak Army, among these people were those who were greedy for profit, there were also bandits and thieves who had slipped through the net, and more were idle scoundrels in the market. Just before the summer harvest, Chang Yuan quietly negotiated the price with the Mongolian army on the other side, preparing to use Jiangyuan County as a letter of surrender to Mongolia, and the Mongols may have promised him to be the commander of Jiangyuan County, and the group of flies and dog thieves under him also had their own rewards.

In Chang Yuan's heart, restoring the glory of the family is the most important thing, as for whether this official is from the Mongol or the Song court, is it so important? He had already calculated in his heart, and made the Jiangyuan County Order, and the first thing he did was to take back the thousands of acres of land and return them to their original owners. The land on the title deed has been reclaimed and has become a first-class fertile land. With land comes a great need for slaves, and those who disobey themselves are an excellent source of slaves.