Zhao Hao has no way to deal with the two little ladies, but can only stay away, and now the armies seem to be marching forward, recovering the lost territory again and again, the situation is very good, and the government and the opposition are still immersed in the excitement of recovering Lin'an, busy receiving the assets in the city, renovating the palace and the yamen to prepare for re-stationing. However, he ordered the reconstruction of the palace hall to be postponed, and no large-scale construction should be allowed, and the reason for this is that in addition to the need for a large amount of financial support, there is also the question of whether to move the capital.

After a series of field investigations, Zhao Yu found that Zhao Gou chose to build in Hangzhou for no reason, Jiankang faced the Yangtze River, if the Yangtze River defense line was breached, Jiankang did not have a defensive depth, and then it fell, this kind of setback often has a great impact on politics and military, and what worries him more is that the Yangtze River defense line he wants to build itself also has hidden dangers that are difficult to overcome.

The Yangtze River is the largest river in China, and its important strategic significance has been recognized by our ancestors since ancient times. As early as the late Spring and Autumn period, the Wu-Chu Water War was already a struggle for control of the Yangtze River, but it had never been a military boundary between the north and the south before the Three Kingdoms. The formation of the Yangtze River defense line is an inevitable product of the situation in the three countries. The confrontation between the Three Kingdoms and the Jin and Wu dynasties was based on the temporary balance of power and the inevitability of historical development.

In the situation where Wei is strong and Wu Shu is weak, Wu Shu will inevitably take advantage of the danger, seek a balance line of power between the two sides militarily, and use the geographical barrier formed by huge mountains and rivers to make up for the weakness and protect himself. At the end of the Eastern Han Dynasty, the Yellow Turban was in turmoil, the world was in turmoil, the Han family was in danger, and the heroes rose together. Sun Jian, Sun Ce, father and son, took advantage of the situation and seized Jiangdong. In the fifth year of Jian'an, Sun Ce was assassinated, and on his deathbed he instructed Sun Quan: "Promote the virtuous and capable, and do their best to protect Jiangdong", and keeping Jiangdong became the foundation of the Sun Wu Group at that time.

Zhao Hao has been planning the strategy of occupying Jiangnan first and then wielding the Northern Expedition in Qiongzhou, so everything is also arranged around this policy. He knew that in addition to the Southern Song Dynasty that he inherited, there was also Sun Wu in the Three Kingdoms period, and although it was maintained for several generations, it failed to keep half of the country in the end. In addition to political factors, relying solely on the Yangtze River defense line from a purely military perspective is also in an extremely passive and dangerous situation.

The natural conditions of the Yangtze River meet the requirements of Soochow shielding Jiangdong. Its main stream traverses central China from west to east, and the upper reaches run in the mountains and valleys of the Qinghai-Tibet Plateau and the land of Bashu, the middle and lower reaches of the river are wide and deep, the river network is dense, and hundreds of tributaries radiate from north to south, becoming a natural barrier. Cao Pi once sighed in Linjiang: "Gutian is so separated from the north and south!" "It is impossible for the northern army to break through and cross the river on the march, but must go through a long period of preparation.

The favorable geographical conditions enabled Soochow to effectively prevent the enemy from crossing south by operating the Yangtze River defense line, and achieved the effect of confronting Cao Wei for decades with the Jiang and Han as pools, and the Huchen resolute soldiers, following the river and defending. Of course, in order to garrison and operate a moat that spans thousands of miles to form a solid military defense line, it is necessary to have sufficient national strength and technical level.

From the point of view of river defense: First of all, it is impossible to defend the river without people. After the development of the Han Dynasty, Jiangdong experienced an increase in population and economic development. In the face of the Central Plains, which had been in war for a long time and was in economic decline, Soochow had an economic foundation in a corner of the country. The more than 200,000 troops of Eastern Wu ensured that all the fortresses on the front of thousands of miles were defended. Sun Quan once said, "If you defend Jiangdong in vain, the soldiers will be self-sufficient." The secession regime, with a population of more than 2 million, enabled it to build a large number of military works and maintain the necessary expenditures.

Secondly, you can't do without boats to defend the river. The great development of shipbuilding technology in the Qin and Han dynasties provided equipment support for the defense of the rivers and rivers of Eastern Wu. The use of anchors, rudders, oars, and sails, as well as the appearance of ship superstructures, have increased the power and mobility of warships, greatly increased the capacity of soldiers and weapons, and enabled warships to use weapons more effectively, especially to carry out fire attacks and launch firearms. In addition, for Soochow, the well-developed water system of the Yangtze River, and the numerous ports, rivers, continents, and Zhu on both sides of the river, are easy to give full play to their advantages in water warfare.

Zhao Hao's strategy in the first stage was to adopt the strategy of limiting the river of Eastern Wu to protect itself, and then to consolidate the Yangtze River defense line with Jianghuai, and finally wave his troops to the Northern Expedition to restore the Central Plains. At present, the Jiangnan region has been developed by the Sui and Tang dynasties, especially after the Southern Song Dynasty regime crossed to the south, and the Jiangdong region has become the richest region in the country, and the population of Jiangnan is more than 100 million, which is much stronger than the economic strength of the Three Kingdoms period. And he also has what can be said to be the most elite naval army and sharp firearms that are at least 100 years ahead of his time, and the conditions for operating the Yangtze River defense line are still in place.

However, the environment that Zhao Yu is facing at the moment is much worse, and in the past, Sun Quan and Liu Bei formed an alliance, so they did not have to worry about the enemy coming down the river from the upper reaches to attack. And now the upstream Sichuan is still in the hands of the Yuan court, and he is not able to recover Shu for the time being. In addition, the Yunnan region on the left flank is also the territory of the Mengyuan Dynasty, and they can repeat their old tricks to attack the Jiangnan region from the flank and rear, so they will be forced to fight on two fronts and divide their troops to defend the Yunnan-Guizhou region.

In addition, at present, due to the failure of the continuous expedition, Meng Yuan's troops have suffered losses and his strength has declined. However, it is important to know that since Kublai Khan succeeded to the throne, he deployed the most combat-ready troops in the northwest to suppress the disobedient kings and protect the Mongol roots. And if Zhenjin can succeed to the throne this time and coordinate the relationship with the various sect kings, he will be able to free up his hands to transfer the army south to Jiangnan.

But Zhao knew that the top priority was to build a defense line on the Yangtze River. According to historical theory, the Yangtze River can basically be divided into three sections: Yizhou in the upper reaches, Jingzhou in the middle reaches, and Yangzhou in the lower reaches. The situation he faced was different from that after the southern crossing, but it was similar to that of Eastern Wu, which did not occupy Shu and only occupied the middle and lower reaches of the Yangtze River. At that time, under the guidance of the national policy of "limiting the river and protecting itself", Soochow carried out a comprehensive military defense of the Yangtze River and built a Yangtze River defense line that ran through the whole territory.

Ready-made things Zhao Hao has always been useless, and he has also done in-depth research on this. The Yangtze River defense line of Soochow bears the sea in the east and blocks the danger in the west, and the Yangtze River controls its districts, and the governor's office is set up along the river to be responsible for defense. The sea and the gorge were the support at both ends of the defense line, and with the strength of Wei Zhou's division at that time, it was not enough to launch a large-scale attack from the sea, and the coastal defense was relatively stable, and the gorge was not necessarily reliable in the same situation as the one he faced.

The Wushan Mountain Range, with an altitude of more than 1,000 meters, connects Daba Mountain in the north, separating Jingxiang and Bashu. The Three Gorges pass through it and rush out. Lu Ji described the topography here: "Its suburbs are connected, heavy mountains are dangerous, and there is no path to a long hub on the land; The river flows rapidly, and the water has the difficulty of shocking waves. "Between the mountains and mountains, the large army could not pass and spread quickly, and it was difficult for the army of Bashu to attack Wu by land.

However, in the waterway, due to the relatively good vegetation protection in the ancient Three Gorges area, there are not many dangerous shoals in the waterway: there are only Qutang and Huanglong two beaches in Qutang Gorge, there are only two places in Wuxia and Shimen, and there are not many dangerous shoals in Xiling Gorge. Although the Three Gorges shipping is not yet mature, people have been able to travel up and down relatively smoothly. At present, Sichuan is still in the enemy's hands, and the natural defense line between the upstream and middle reaches is roughly in the area from the Three Gorges to Yiling, that is, Zhao Yu wants to try his best to seize Jiangling in Jingzhou, which will be the starting point of his defense line.

In addition, Soochow set up military towns in all important strongholds on the Yangtze River defense line, and military town governors were also set up in some places. They successively set up more than 20 military and town governors, most of whom were located along the Yangtze River. Although all the military towns on the Sun-Wu Yangtze River defense line were deployed and garrisoned, they were not isolated from each other. The entire line of defense is not divided by the governors of each military town, but an organic whole. According to the needs of the war situation, the military and town governors can sometimes act alone, and sometimes several military and town governors can act separately to coordinate with each other.

According to the national policy of limiting the Yangtze River to protect itself and the military geography of the Yangtze River defense line, Zhao Hao thought that the dangerous places for the entire middle and lower reaches of the Yangtze River defense line were mainly Xiling, Puqi, Wuchang, Wankou, Niuzhu, Misu, Jianye, etc. The strategic places with overall significance are roughly focused on Xiling, Weixu, Wuchang, and Jianye, that is, the four places of Jiangling, Wuhu, Ezhou and Jiankang that he is eager to occupy at present.

As far as the entire defense line was concerned, nothing more troubling the ruling group of Sun and Wu was the enemy's breakthrough of its upstream defense line and the eastward movement of the army down the river, both by land and water. In this way, "the danger of the Yangtze River has been shared with us", the effectiveness of the Yangtze River moat was lost, and the entire defense line was completely exposed to the enemy's military attack. Therefore, Xiling, located at the western end of the Yangtze River defense line, became the first important military town on the Yangtze River defense line for thousands of miles.

For this reason, Lu Xun once went to Sun Quan and said: Yiling is critical, and the country's borders are easy to obtain, but also easy to lose. If it is not a county in vain, Jingzhou is worried. His son Lu Kang also believed: Xiling, Jianping, the country's feudal table, that is, in the lower class, the enemy two realms. If the enemy is rafting down the river, sailing thousands of miles, the stars are running to lightning, and Russia is coming, it is necessary to help other departments to save the county. This is an opportunity for the safety of the community, and it is not a small harm to invade the tomb in vain. In view of the important position of Xiling, Sun Wu set up a heavy army here, set up a governor to command, and all of them were famous generals to suppress Wu.

As the first military town governor set up by Sun Wu, it is another important military town of overall significance on the Yangtze River defense line of Sun Wu. The source of the wet beard is out of Chaohu Lake, flows southeast through Wuwei, enters the Yangtze River in the east, and the entrance is the mouth of the wet beard. Baojiang will fight for Huai, heavy troops stationed in the wet beard, advance can be attacked, retreat can be defended, offensive can rely on Sun Wu elite sailors out of Chaohu, attack Hefei.

Hefei was a place where Wei and Wu fought for during the Three Kingdoms: Wu occupied Hefei to shake the Central Plains; Wei according to Hefei, Wu Zhi and Xu Huai were not at peace. Therefore, the war between Wu and Wei was mostly focused on the battle for Hefei. If the wet beard is lost, Cao Wei can go east along the river, and go to Jianye at night and evening, which is the risk of Wu's death.

Jianye was the place where Sun Wu rose, and it was used as a place of governance, and Wuchang was also used as the capital. Sun Wu's rule here had a solid foundation, and the interests of the wealthy landlords in Jiangdong were also concentrated in the vicinity of Jianye; And here the Yangtze River is wide and vast, located in the water town of the south of the Yangtze River, the river bay crosses, and the Jili water division is stationed, "there are more than 100 miles of small rivers in Moling, that is, there is an emergency, you can install a big boat, and we manage the water army."

However, Jianye is located in the lower reaches of the Yangtze River, far from the upstream defense line, and it is difficult to reinforce in time once there is an alarm. Wuchang chokes the middle end of the Yangtze River defense line of Sun Wu and Wu, which can rescue Xiling and prevent Cao Wei from plundering Nanjun in the south; It can respond to military operations in Anhuikou, Maoxu, Niuzhu and other places; At the same time, it can also lead the army through the Han River, go north to attack Xiangfan, and then deter the Central Plains.

Sun Wu relied on Xiling, Weixu, Wuchang, Jianye and other important military towns to choke the Yangtze River defense line in dangerous places, in order to become a hub, up and down the strategy. In addition, there are also many ships of the Yangtze River cruising up and down the Yangtze River, just in case, and the entire Yangtze River defense line echoes up and down, in one go. He also deployed heavy troops along the Yangtze River, relying on the Yangtze River in its territory to form a defense line that could not be easily crossed, so that Sun Wu was able to establish the country in the east of the Jiangdong, reject Cao Wei in the north, and resist Shu Han in the west.

However, Sun Quan was not completely willing to just "keep Jiangdong", and wanted to advance to Jiangbei and compete for Jianghuai. Historically, if the southern regime could not push its borders to the Huai River, but instead held the Yangtze River, it would have been in a dangerous position. At this time, it had only one line of defense, and if the northern army broke through the Yangtze River, it would have to wait for its hands to be killed. If an effective line of defense can be established along the Huai River, the situation will be much safer.

If the northern regime wants to capture the south of the Yangtze River, it will have to spend a lot of money to break through the first line of defense, and then cross the Huainan waterway, which will consume a lot of strength of the northern army, and sometimes it will have collective diarrhea if it is not done well. By the time they arrived at the Yangtze River defense line, it was no longer useful. Moreover, it is not easy for them to organize a boat crossing the river on the spot after crossing the thousand-mile line of fire. At this time, the northern army can often only look at the beautiful scenery of the Yangtze River, and when the weather is good, they may be able to look at the Jiangnan chicks on the other side, and then they can go home.

Therefore, the war between Soochow and the north basically took place in the area from the Huai River to the Yangtze River, and the two sides repeatedly fought for several cities on the border, surrounded by trenches, flooded, sabotage, and rebellion, and made all kinds of bad ideas that hurt each other's skulls. The loss of Jianghuai caused the Soochow regime to implement a strategy of limiting the river to protect itself, and the retreat of the defensive line exposed the capital of Soochow to Jianye (Jiankang) to the enemy.

Zhao Yu also knew the truth that defending the river must defend Huai, but although Jiangnan has recovered most of the area at present, there are still remnants of the enemy occupying the city, and it takes time to divide troops and time to pacify it. Even the Yangtze River defense line, which he tried his best to establish, only captured a few important towns in the lower reaches, and Ezhou and Jiangling in the middle reaches were not recovered. Therefore, they are not yet able to fight for the Jianghuai region, and even Xiangfan, which is the top priority, will be difficult to hold even if they occupy the Jianghuai region if they cannot control it......