Zhao Yu conducted a study of Sun Wu's Yangtze River defense line because he was similar to the situation he was facing, but after a thousand years, the vicissitudes of the sea and the situation changed, and he knew that these could only be referred to, but he could not copy them in a rigid way. However, there are many people around him who have witnessed the loss of the Yangtze River defense line in this dynasty, and he has also done in-depth discussions and analysis with them, hoping to get something useful from it.

But the results obtained were varied and different, and Wenchen blamed the generals for refusing to use their lives and defecting in battle; Military generals rely on civil officials who only know infighting, do everything to elbows, and are greedy for life and afraid of death. There are also people who think that the powerful ministers manipulated their authority, expelled dissidents, suppressed good ministers and fierce generals, and destroyed the Great Wall; Some people also say that corruption in the imperial court has become a common practice, and the civil and military generals only know how to make money in their pockets by unscrupulous means, which leads to the boiling of public resentment, and the officials do not want to serve the country, and will not want to serve the territory.

Of course, Zhao Yu still knew that they had some things to say, but the subtext was that the emperor was mediocre, appointed traitors, and wasted the country extravagantly, so that their reputation was boring, but they didn't dare to say these things clearly, and they could only think that they didn't understand. Anyway, the result is that no one is responsible, and he is the most wronged one, but he knows that the biggest reason is that because of 'money', the Song Dynasty is unwilling to destroy this good life from top to bottom, and would rather be in the south of the Yangtze River, and the heart of recovering the country has faded. So whoever mentions the Northern Expedition will be unlucky, and whoever wants to restore the country will step down, but this can be said to be in line with the public opinion from top to bottom.

However, Zhao Yu felt from everyone's mouths that the Southern Song Dynasty's defense in the Jianghuai area, the Huai River, the canal and the Yangtze River played a great role. The Huai River is the first line of defense, and the estuaries of the lower reaches of the Huai River are mostly the focus of defense, especially in the Shanyang and Huaiyin areas where the Yellow River flows into the Huai River. Therefore, the focus of the defense of Huaidong in the Song Dynasty was to deploy along the line from the canal to the Huai River. In particular, Chuzhou and Zhenzhou, which are the places where Huaixi and Huaidong are connected in transition, facing Nanjing to the south; It is also an area that may be captured by the northern army after crossing the Huai River from the west or east of Huai.

The Yangtze River has always been valued by the Song court, not only the last line of defense and the Song army needs to be desperate, but at the same time, the Song Dynasty also realized that it has a certain advantage on the Yangtze River, and often has the possibility of turning the tide of the war. First of all, the Yangtze River can be used, and the garrison in the upper reaches of Nanjing can quickly assemble reinforcements, calmly withdraw south along the canal, and redeploy defenses north of Zhenjiang; In addition, along the canal in the south of the Yangtze River, the army of the south of the Yangtze River can be gathered in Zhenjiang and Taizhou; Even the armies of Jiangsu and Zhejiang could enter the Yangtze River along the coastal road.

Therefore, the convenience of the Yangtze River and the canal allowed the Song army to quickly mobilize military forces in the south of the Yangtze River and even in the larger hinterland of the Jianghan Plain; Of course, the materials of the nearby rich Poyang Lake Plain, the Ganjiang River Basin and the lower Yangtze River Delta Plain can be easily assembled to ensure military supplies; Then there is the advantage of the Song army's naval army, in the Huze and canal areas, the northern superior cavalry can not be used, although the northern army from the southeast of Huai, and there is a plan to cross the river, the initial preparation of ships will not be many, more ships need to arrive at the north bank of the Yangtze River after stepping up manufacturing, in a hurry, the northern army's naval division will not have an advantage.

On the other hand, Zhao Yu asked about the court, whether it is the important ministers of the court, the senior generals, and those famous people in the opposition, they all have special respect for 'guarding the river must guard the Huai', thinking that in order to keep the south of the Yangtze River, it is necessary to seize the Jianghuai and ensure the land of Jingxiang. He also did some homework on this, and felt that it was not unreasonable. The Jingxiang region and the Lianghuai region, due to their geographical convenience, had the superior conditions of being able to support each other's defense, and this strengthened the confidence and superiority of the Southern Song Dynasty in effectively blocking the northern army in the wide area between the Huai River and the Yangtze River.

Of course, the premise for the realization of this condition is that the defense of Xiangfan on the Jingxiang side must be stable. Because only in this way did the armies in the Wuchang and Ezhou areas, which were originally the support bases of Jingxiang, including the armies in the Huang, Qi, and Shu directions in northeastern Hubei Province, respectively divided their troops from the plain areas on the north bank of the Yangtze River to the east to reinforce the battle between the two Huai and the Yangtze River, and the troops under Yue Fei had reinforced Huaixi from the south of the Dabie Mountains to the east.

Moreover, Jingxiang and Lianghuai themselves also placed troops reinforced between the two places, which were the troops stationed in Jiangzhou and Chizhou, and their task was to prevent the northern army from crossing the Dabie Mountains from the Gwangju area north of the Dabie Mountains, and sneak attack the south to cross the river between Ezhou and Jiangzhou, which the Jin army did in the early Southern Song Dynasty; Another task is to act as a mobile force to reinforce Huaixi; In peacetime, it serves as an important force to stabilize the defense line of the Yangtze River.

Zhao Yu has not had the opportunity to inspect the Jingxiang area in his life, and even now he has only walked around the mouth of the Yangtze River, let alone set foot in Jingxiang, and can only get what he needs from various predecessors' notes and other people's mouths, so it is more like talking on paper. However, there are no airplanes at this time, let alone satellite maps, and the vicissitudes of life, everything has changed a lot from what I know, so I can only rely on books and my own brain to make up for it.

According to Zhao Hao's analysis, there are three locations in the Jingxiang area that were valued by the Song people, Xiangfan, Ezhou, and Jiangling, the most important of which are Xiangfan and Ezhou, and the strategic location of the latter two was particularly important in the period of the confrontation between the north and the south in ancient times. When people compare Sichuan, Shu, Jingxiang and Lianghuai, they mostly regard Jingxiang as the center and the backbone, and regard Chuanhuai as the two wings. What he didn't quite understand was that the large-scale wars of the Song and Jin were mostly in Lianghuai, and the Jin army rarely placed the main force of the southern attack in the direction of Jingxiang.

However, by piecing together the maps of various regions, we can understand the status and strategic significance of Xiangfan and Ezhou in the military defense of the Yangtze River. First of all, the Lianghu Plain is an important agricultural economic zone in the south, and Xiangfan is the northern gateway of the Jianghan Plain, Xiangfan and the cities along the Han River to the south, Yingzhou, De'anfu, Huangpi, etc. constitute the defense support of the Yangtze River and the north of Ezhou.

Zhao Yu also understood the loss of Xiangfan and the north bank of the Yangtze River, so he moved his whole body like a trigger, which would enable the northern army to go down the river and approach Jiankang. In this way, the defense of the entire Huaidong and Huaixi will be self-defeating, and the armies of the two Huai can only finally withdraw to the south bank of the Yangtze River, trap Jiankang in one place, break the original balance of mutual holding, and turn it into a confrontation across the river, so that the southern army will fall into a comprehensive passivity.

In addition, the Jianghan Plain was also an important economic zone in the Southern Song Dynasty, and when the Northern Army completed the occupation of this area, its economic power would be greatly enhanced, and the economic power of the Song Dynasty would be greatly weakened, and the pattern of attack and defense and victory and defeat would be determined.

In fact, even if the Yuan army was blocked many times at Diaoyu City and Lianghuai in Chongqing, and once it broke through Xiangfan and Ezhou, the battle between Sichuan and north of the Yangtze River was over, and the battlefield of the decisive battle between the Song and Yuan dynasties was also switched to the west of Jiankang, and it was difficult for the Song army to turn the tables around. Therefore, Zhao Yu felt that this battle also proved the law that Xiangfan and Ezhou existed, then Sichuan, Shu and Lianghuai could be safe, and Jingxiang was lost, and Sichuan, Shaanxi and Jianghuai would be difficult to protect.

Zhao Yu looked farther and made more discoveries from the map, he felt that the Jingxiang area was not only protected by the Han River and the Jianghuai area south of the Dabie Mountain, in fact, the Song and Jin Dynasty were demarcated along the Qinling-Huaihe line, and the boundary was not in Xiangyang, but in the Nanyang Basin and the northern foot of the Dabie Mountain, this area was still the front line of the Song army's protection, that is to say, the Han River and the Dabie Mountain were not the first northern defense areas of the Southern Song Dynasty, and should go further north.

In this way, the importance of Xiangyang's position is not limited to the Jianghan Plain behind it, but extends forward, ensuring the security of the Han River Corridor on the left side, that is, the connection between the Sichuan-Shaanxi Theater along the Han River Corridor and the Jingxiang and Jianghuai Theaters, and also preventing the Northern Army from making a detour from Wuguan Road to the Han River Corridor through the west side of the Nanyang Basin. At the same time, the stability of Xiangyang as an important military town is conducive to the control of the Nanyang Basin by the southern forces, and the importance of the Nanyang Basin to the Central Plains is self-evident. Relying on Xiangyang and striving for the initiative in the Nanyang Basin, the Jingxiang Theater will be able to establish a solid cooperative defense relationship with the Huaixi Theater at the northern foot of the Dabie Mountains.

The area of defense between Jingxiang and Lianghuai in the Southern Song Dynasty was expanded, and not only the terrain of Xiangyang City and Dabie Mountain was passively used to defend, but at the same time, the joint defense of Jingxiang and Lianghuai, especially Huaixi, was optimized. Therefore, the significance of the military activities of the Southern Song Dynasty north of Xiangyang and north of the Dabie Mountains cannot be overlooked, and the results of the military activities north of Xiangyang lie in the fact that the entire Sichuan-Shaanxi and Lianghuai theaters have been strengthened from both sides, and the ties between the three theaters have become closer, so that the Jingxiang theater can provide timely and effective support when the war is concentrated in Sichuan-Shaanxi and Lianghuai, especially Huaixi.

On the contrary, if Xiangfan is lost, not only will the defense of the northern foot of Dabie Mountain cease to exist, but also the situation of Dabie Mountain as a mountain danger will also be lost, not only will Jingxiang's army have to fully retreat to the Wuhan River, but at the same time Lianghuai will also lose the protection on the left side, and the necessity of defense north of the Yangtze River will also cease to exist; The armies of the two Huai will also be forced to abandon the Huai River and the vast area south of it, and will have to assemble on the Yangtze River south of Jiankang to prepare for the northern army to advance eastward along the Yangtze River and its banks from the direction of Wuhan.

In addition, the consequence for the Sichuan theater was isolation. The loss of Xiangyang may cause the collapse of the Qinling defense line in the Sichuan-Shaanxi Theater, so that the original army will withdraw south to Micang Mountain to set up defenses, and it will have to defend the army in the east that may be preparing to enter Sichuan from the west of Xiangfan, so that the defense in the direction of Chengdu will naturally be seriously weakened. The northern army could move south along the Han River and soon threaten Jingmen and Yichang. In this way, the Sichuan Theater was caught in the front and rear, not only could it not return to the lower reaches of the Yangtze River, but it also fell into a situation of sitting back and waiting to die because it was cut off from the lower reaches.

And Zhao Yu looked through the battle examples between the Song and Jin dynasties and the Song and Mongolia at that time, and the situation in the late Southern Song Dynasty was basically in line with this. It is no wonder that in the middle and early period of the Southern Song Dynasty, although the war in the direction of Xiangfan was far less tense than that in Huaixi, many Southern Song ministers believed that the most important defense focus related to the survival of the Southern Song Dynasty was Jingxiang. And once this place was lost, the Song court not only lost a buffer area, but also lost the advance position of the Northern Expedition to the Central Plains. And he knew that after the Huaihai Campaign in later generations, the Yangtze River defense line of the national army was completely exposed, and he was finally expelled from Jiangnan and took refuge in Taiwan.

In addition, everyone understands that fighting a war is burning money, and money is not blown by the wind. Therefore, although the layout of mountains and rivers is fixed, the significance of their military geography depends on the differences in the relationship between economic regions, as well as the distribution of political power boundaries and the mutual relations between political regimes.

The Jianghuai region is economically developed, and the control of this region is not only a change in the size of the region, but also a change in the population, taxation and other important economic forces within the region. Therefore, when it comes to the contention of important economic zones, the balance of power between the two sides of the war is very rapid, especially when the situation is evenly matched, and it is very obvious when fighting for a region with important economic influence. There are countless examples of this kind, most of the areas occupied by the Eighth Route during the anti-Japanese resistance were poor and remote areas, and it was difficult to make great progress, but once it occupied the northeast, the situation immediately changed greatly, and there was no shortage of people and guns.

In the same way, Xiangfan's military value also lies in its control of the rich area of the Jianghan Plain. If Ezhou falls, the regime in the lower reaches of the Yangtze River will lose its economic control from Sichuan, Yunnan, Guizhou, Hunan, and even Guangzhou. With the fall of Ezhouru, Jiangzhou, which is not far to the east, is almost unsafe, but the loss of Jiangzhou means the loss of the Ganjiang River Basin. Therefore, when only the economy and manpower of the Taihu Plain in the delta south of the lower reaches of the Yangtze River remain, it is impossible to recover the defeat.

Zhao Yu actually understands that the length of the Yangtze River is thousands of kilometers, and in some places where the river is relatively narrow, it is actually easy to cross the river, and the important thing is that this military buffer zone north of the Yangtze River and south of the Huai River, if the Huai River is lost, the Yangtze River will be difficult to protect, so militarily there is a saying that 'the limit of the Yangtze River cannot be held for a long time'. At present, the situation he is facing is that not only does he not have Jianghuai as a buffer, but there is not even a foothold on the north bank of the Jiangjiang, and theoretically the Yuan army can attack them from any point.

It can be said that the situation facing Zhao Hao at the moment is even more dangerous than in Qiongzhou, although the Qiongzhou Strait is not wide, but it is also wider than the Yangtze River; And even if it is counted from Jiangling, the middle and lower reaches will be thousands of miles, and the defensive front will be ten times longer than that of Qiongzhou; And he used to manage only a place with a population of less than a million, but now it is a hundredfold increase, and the pressure is huge. Therefore, the current situation seems to be very good, but it is full of difficulties and dangers, whether he can complete the goal of consolidating the defense of the Yangtze River and stabilizing the south of the Yangtze River, and not be driven back to Qiongzhou by the reappearance is a great test for him and the dynasty......