This naval force, consisting of 5,000 ships and 70,000 men, trained in the upper and lower reaches of the encirclement line. The outskirts of Xiangfan have been transformed into a training ground for Mongolia's "land and water army".

The Mongol army was different from the past, and put on a posture of staying for a long time, and after this news reached the Southern Song court, it caused great shock. The prime minister of the Southern Song Dynasty, Jia Yidao, was well aware of the importance of Xiangyang to the Song Empire, and sent reinforcements north twice before and after, but they were repelled by the Mongol army. In June of the seventh year of Xianchun (1271), Jia Rudao once again sent 100,000 mobile troops led by Fan Wenhu to set off north along the Han River, which could be described as the ace army of the Southern Song Dynasty.

The Mongols have been waiting for this day for a long time. On the basis of the three types of land combat units, pure cavalry, mixed infantry and cavalry, and pure infantry, plus the newly organized naval army, the Mongolian army used various fortresses and fortresses to set up huge combat positions, so the Southern Song Dynasty army's move was tantamount to throwing itself into a net, the land and water were defeated, the main force was all destroyed, and Fan Wenhu fled alone.

As a result, the Southern Song Dynasty fell into a disadvantage. As the ace troops were routed by the Mongol army, the entire Southern Song Dynasty fell into panic. After that, the Southern Song Dynasty, as a state and regime, did not take any rescue actions (some of which were successful) to save the situation.

During these difficult days, Lu Wenhuanli encouraged the soldiers and people of the two cities who were surrounded and isolated, while struggling to support the situation.

At this time, Kublai Khan began to put into use a new weapon, the "Huihui Cannon".

In January of the ninth year of Xianchun in the Southern Song Dynasty (1273), a huge trebuchet appeared on the outskirts of Fancheng, and a huge stone projectile destroyed the wall of Fancheng, and the Mongol army entered the city, and Fancheng fell. Subsequently, the trebuchet that moved into Fancheng set its sights on Xiangyang.

The terrifying huge stone projectile easily crossed the wide Hanshui River and struck Xiangyang from above. The Hanshui, located between the two cities of Xiangfan, was also 700 to 800 meters wide, and at that time this weapon had at least such a flight range. Unlike bows, ballistas, and firearms, its attacks are simply not able to withstand them. Under the terrifying power of this new weapon that could destroy the towers, military houses, and houses one by one, and sweep away all the defenders and civilians, Lu Wenhuan began to want to give up. Finally, in February of the following year, on the condition of preserving the lives of the whole army and all the people, Lü Wenhuan Kaicheng surrendered.

Kublai Khan treated Xiangyang very favorably, not only did not kill a soldier or a single citizen according to the previous agreement, but also appointed Lü Wenhuan as the "Governor of Xianghan", with absolute military power in the Han River Basin, and his soldiers were also awarded the status of "Guards and Guards" directly under Kublai Khan, and were commanded by Lü Wenhuan as before.

This is an unbelievable preferential treatment for Lu Wenhuan and his subordinates. First of all, it was the enemy Mongols who spoke highly of their six-year battle to defend the city; Secondly, they were given the privileges of being a direct force of the Mongol Great Khan, a larger sphere of influence than before, and were evaluated as the best brave men, which was the highest honor for those who practiced martial arts. The gratitude of Lu Wenhuan and his soldiers is natural, and the joy of the family and the people is also natural. In the battle to defend the city, the two armies suffered very few casualties, so there was no hatred between the Mongol army and Lü Wenhuan's army, and even naturally developed feelings of fighting side by side. The bloody carnage that usually accompanies war was almost absent in this campaign.

On the contrary, Lü Wenhuan's army and the people of Xiangfan began to lose trust in the Southern Song court. For Lu Wenhuan, especially after the death of his cousin Lu Wende in the battle to defend the city, Jia Yidao's attitude was as if he wanted the entire Lu clan to be annihilated, and even deliberately abandoned them. Of course, this was not the case, but Jia Rudao's extreme helplessness at that time and the suspicion of the Southern Song Dynasty court from beginning to end triggered their association.

Suspicion then overcomes anger and escalates directly into a revenge mentality. At this time, the difference between those who abandoned themselves and those who recognized them, between the Southern Song Dynasty court and the Mongol Empire, was clear at a glance. There were many Han Chinese working for Kublai Khan under Kublai Khan, and the verbal scholarly arguments rarely appeared, and the "party struggles" between literati and bureaucrats who relied on flowery rhetoric to disguise themselves rarely occurred, compared to the Southern Song Dynasty court in Lin'an, which was full of infinite jealousy and struggle from top to bottom, including scholars, Kublai Khan can be said to be "perfect" here.

Lü Wenhuan and his corps pledged their loyalty to Kublai Khan, and naturally applied to serve as the spearhead of the next round of the war against the Song Dynasty. However, the Mongolian side's arguments or evaluations about the "defection" and "betrayal" of Lü Wenhuan and others have almost never appeared.

And Lu Wenhuan's "apostasy" decided the fate of the entire Southern Song Dynasty.

Before the Mongol army attacked, the Southern Song Dynasty's defenses had already begun to show a tendency to disintegrate. In any case, Lü Wenhuan, who had a high reputation in the Southern Song Dynasty for resisting the Mongol attack, was treated favorably by the Mongols and was willing to serve the Mongols, which undoubtedly became the best example.

Subsequently, the Mongol army was overwhelmed, and it took only a year to make complete preparations. The battle line stretched from Huaidong to Sichuan, covering the entire north-south border. If the battle of Xiangfan was an attack and defense of "points", then after the war entered the second stage, it became an attack and defense of "surfaces". In the first month of the tenth year of Xianchun (1274), the Mongol army won in Ezhou without a fight, and all the defenders of the Southern Song Dynasty opened the city gate to the Mongols. The commander of the Mongol army, Boyan, gave the surrendered army a high courtesy, and let each of them stay in their original posts, and at the same time sternly warned the soldiers of his army not to plunder a single penny, not to harm a soldier or a people, in this way, Ezhou and its surroundings were quietly absorbed by Boyan. Since then, Mongolia has gained a foothold south of the Yangtze River for the first time, and it is an extremely important foothold.

In March of the 11th year of Xianchun (1275), the prime minister of the Southern Song Dynasty, Jia Rudao, made a desperate gamble and personally supervised the division to Wuhu, at this time the Southern Song Dynasty still had more than 2,500 warships, but the army had lost its unified command and desire to fight. Boyan first sent Mongol cavalry to both sides of the Yangtze River, and then used warships to launch a fierce attack. The Southern Song Dynasty army soon became disorganized, and the general Xia Gui was the first to escape. The stunned Jia Rudao Mingjin withdrew his troops and tried to stop the fleeing soldiers, but to no avail, the whole army collapsed instantly. The fate of the Southern Song Dynasty also came to an end, and Jia Rudao was held accountable for his defeat and killed on the way to exile.

Since the departure of Boyan's army from Ezhou, it finally reached Lin'an, the capital of the Southern Song Dynasty, without a single hand-to-hand battle. In the first month of the thirteenth year of the Yuan Dynasty (1276), the Southern Song Dynasty court and the royal family surrendered to the Mongol army Kaicheng, and this surrender was unusually peaceful, and many Lin'an people did not even know about it.