After Xia Xue told Li Shimin about Emperor Yang of Sui's conquest of Goguryeo, she and Li Shimin analyzed the reasons for their failure. Xia Xue also added the reason why Li Shimin's personal expedition to Goguryeo was not successful in the end in the history books.

The two of them finally decided, first, this expedition to Goguryeo can not use too many troops, but not too little, after all, Goguryeo is not like the Turks do not have cities, Goguryeo after hundreds of years of development, there are many strong cities and dangerous passes in the country, this time it is more of a fortified battle, and it is necessary to send troops to occupy and manage after it is defeated. After the two discussed, it was decided to dispatch 100,000 elite soldiers to the main force of the mobile warfare, including 80,000 in the army and 20,000 in the navy. In addition, the 200,000 auxiliary corps, which mainly defended and occupied the city, followed behind the main battle corps and arrived at the war zone by land and water in batches.

Second, due to the heavy losses of the Sui Dynasty's conquest of Goguryeo, hundreds of thousands of dead and wounded soldiers and horses, which became the psychological shadow of the people in the Guannai, in order to prevent the forced conscription from arousing the same public anger as the Sui Dynasty, this time the main force corps and the auxiliary corps both adopted the "recruitment method" to voluntarily sign up, and set up a volunteer army to recruit Liaodong, and the imperial court will issue weapons, military salaries, clothing, tents, food, etc. to the volunteers who signed up, and those who performed well will also be rewarded and promoted. Li Shimin and Xia Xue originally thought that the number of volunteers who should sign up for the conquest of Liaodong would not be very large, but they did not expect to get the news that the officers and soldiers of the Tang Dynasty and the people were enthusiastically signing up, and many places exceeded the upper limit of the number of recruits, and they all wanted to avenge the hundreds of thousands of officers and soldiers who died in the Sui Dynasty's conquest of Goguryeo in the past.

Third, in order to alleviate logistical pressure and prevent difficulties in the supply of grain and grass over long distances, in this conquest of Goguryeo, in addition to carrying a large amount of grain and grass, the land troops also brought with the army a large number of livestock, such as cattle and sheep, which mainly ate grass. In this way, cattle and sheep can march with the army, and they can also carry baggage along the way, which can greatly reduce the burden on the soldiers and the state capital along the way, and can also reduce the slowness and difficulty of long-distance transportation of grain and grass.

Fourth, the corps of the main force of the battle was all equipped with war horses, and now it has conquered the Turks and has the steppes. The army is no longer short of war horses. This would alleviate Don. The physical exertion of the army's long journey can also speed up the marching process, shorten the time to conquer Goguryeo, and prevent protracted and stalemate warfare. The auxiliary corps is dominated by infantry.

Fifth, "go to the army to fight and plot", in order to prevent the Goguryeo people from stubbornly resisting, increase the number of Tang. The army suffered casualties, and during the conquest, the policy was vigorously publicized to the people of Goguryeo: surrender without killing, give preferential treatment to prisoners, and give rewards to those who voluntarily sacrifice the city.

Sixth, prepare winter cotton clothes, cotton hats, cotton gloves, leather clothes, charcoal, coal and other winter clothes and heating materials in advance, take precautions and prevent accidents, in case the cold winter in the Northeast comes in advance, freezing to death and frostbite Tang. army, and is ready to continue the offensive in the winter, so that Goguryeo will not have a chance to breathe.

Therefore, due to the fact that the special forces of the Angel Army could not get out of the conquest of Nanzhao, in this campaign of conquest of Liaodong, the army was mainly armed with cold weapons such as bows, arrows, knives and spears. The army is dominated by infantry and cavalry.

The Tang Emperor Li Shimin issued an order to conquer Goguryeo, and the war machine of the Tang Dynasty was running at high speed, and the quilt factories for making cotton clothes and quilts were fully opened, and several new ones were built, and the production efficiency was also greatly improved under the drive of steam engines, internal combustion engines and electric motors.

Grain, grass and ordnance have been raised in large quantities and slowly transported to the northeast border by land and sea, including various cans invented by Xia Xue that can store vegetables and food for a long time to increase the nutrition of the expeditionary force.

Xia Xue recommended to Li Shimin to let Liu Renliang, the Cheng of Liyang County, serve as the commander of the Tang Dynasty Naval Division that attacked Goguryeo and Baekje, although Li Shimin did not know why Liu Renliang, a small county that was not very famous, why Empress Changsun valued it so much, but Li Shimin has always had absolute trust in Xia Xue, although many ministers also did not understand and objected to Liu Renliang, a small county Cheng, as the commander of the Tang Dynasty Naval Division, but Li Shimin overrode public opinion and still appointed Liu Renliang as the commander of the Tang Dynasty Naval Division to conquer Goguryeo and Baekje. This appointment surprised Liu Renliang himself, and he was surprised and delighted, but Liu Renliang, who had great ambitions, was unwilling to let go of this great opportunity, and immediately happily took up his post, and worked day and night to learn about the knowledge of the navy division and navy, and strive to become an expert in naval warfare and water warfare.

Of course, Xia Xue knew Liu Renliang's name, which he knew from the history books when he was in school. Liu Renliang, born in 601 A.D., was born in Bianzhou Weishi, is a famous general in the history of Huaxia into the phase of the figure, he was a late bloomer, but a blockbuster, Liu Renliang commanded the famous Baijiangkou naval battle in history, with less to win more, defeated the Fusang navy, resulting in the overall Tang Dynasty of Fusang, to learn from the Tang Dynasty.

Liu Renliang is a famous old birthday star in the history of Huaxia, at the age of 84, he was young in the turbulent times at the end of the Sui Dynasty, and his family was poor, unable to concentrate on studying, but he never gave up on himself. Without pen and paper, he practiced writing on the ground with a branch, and actually read through literature and history, and was famous for his erudition. At the beginning of Wu De, the ambassador of the Central Plains Province, the prince of the state of China, Ren Gui was ready to discuss things, Liu Renliang saw his manuscript on the table, revised a few words for him, Ren Gui was very surprised, and saw that Liu Renliang was quite literate, so he let him join the army in Xizhou in the way of Chi Mu (the Red Conferral was the system of the early Tang Dynasty, according to the normal procedure, it should be the official state of the Ministry of Officials with a red pen, the Ministry of Men approved by the province, and the emperor finally granted the decree). Soon, Liu Renliang was transferred to Chen Cangwei. There is a local lieutenant named Lu Ning, who is rampant, and no one in the former magistrate dares to care about him in Yumeat Township. The Zhichong Captain belongs to the Zhuwei Zhichong Governor's Mansion, and the Zhichong Captain of the Lower Mansion is all the lower rank of the fifth grade, and the status of the little Chen Cangwei is far from it. However, Liu Renliang was businesslike and gave the uncle a stern warning, but Lu Ning didn't pay attention to it and still went his own way. When he violated the law again, Liu Renliang arrested him and had him beaten to death with a stick. When the news was reported to the Tang Emperor Li Shimin, the Son of Heaven was furious, "A small county lieutenant dared to kill me with a cane, it was simply lawless."

Tang Taizong summoned Liu Renliang, and quickly figured out the merits of the matter, and in the face of Liu Renliang's eloquent talk, a generation of famous monarchs was greatly impressed, and immediately promoted him to Liyang County. Tang Taizong likes to hunt, one year, Tang Taizong planned to go to Tongzhou (the three Qin Dali of the later generations) to hunt, Liu Renliang timely to the emperor on a twist, "this year the wind and rain are smooth, the crops are growing gratifying, the people work hard day and night, only to harvest one-tenth, two, now the emperor goes to hunt, all kinds of reception plus repair bridges, often use one or twenty thousand labor, the harvest of the people is quite unfavorable." If the people are harvested, the emperor will shoot and hunt again, both public and private, can take into account", Tang Taizong knew that his mistakes must be corrected, and postponed the hunting operation for a whole month, and he issued an order to praise Liu Renliang's admonition, "Although your official position is not high, you are dedicated to the people, and the things you have stated have won the hearts of the king."

Xia Xue pinched her fingers and calculated, Liu Renliang was just 30 years old this year, which is the golden age of men, so she recommended Li Shimin to promote Liu Renliang, who was not very famous, so that he could make contributions to the Tang Dynasty early.

On this expedition, after discussion, Li Shimin and Xia Xue decided to divide their troops into three routes:

One route was led by Li Jing to lead 10,000 elite cavalry of the Angel Army to attack Goguryeo from the western grassland, and on the way he could absorb some Turkic, Khitan and other tribal knights to increase his troops. Moreover, it also has the role of cutting off the reinforcements of the Xueyantuo Khanate, this time Goguryeo not only colluded with Baiji and Fusang, but also colluded with the Xueyantuo Khanate in Mobei.

One way was by sea, with 1,500 navy and 30 steel warships led by Qiu Huke assisting the 15,000 naval forces of the Tang Dynasty led by Liu Renliang to land and attack Pingyang City, and covering a large number of auxiliary soldiers and heavy ships to land on the beaches of Goguryeo and Baekje. In addition, there were many large sailing ships and turbine cargo ships accompanying the logistics transport, transporting food and grass supplies, and a large number of auxiliary soldiers.

One route was led by the Tang Emperor Li Shimin to lead 70,000 main battle corps, and after leaving the Yuguan (Shanhaiguan), he attacked Goguryeo from the front.

In addition to Li Jing, who crossed the West Road, there was no auxiliary corps, Li Shimin's 150,000 follow-up troops on the Middle Road, and 50,000 people in the auxiliary corps of the follow-up troops of the Datang Navy on Liu Renliang East Road, were also ready to go.

When Li Shimin set out on the expedition, Xia Xue carried the child to Tongguan, and the two hugged each other for a long time, bursting into tears, and it was difficult to give up. It is said that if the military affairs are not urgent, they will exchange information through telegraph every day.

"Husband, I believe you are the best! You're going to be victorious! Xia Xue looked at the back of Li Shimin, who was gradually moving away, and said softly.

The Sui Dynasty failed to conquer Goguryeo three times, and Goguryeo built the bones of the fallen soldiers of the Sui army into a Jingguan. (In ancient wars, in order to show off their martial arts, the victor collected the corpses of the enemy, and the high mound made of sealed soil was called "Jingguan") "The body is dead and buried in Shanyang." The mountains are majestic, and the sky is vast. There are trees in the mountains, and there are mourning in the country. The soul returns, in order to see the rivers and mountains. "The cold wind blew, and the thin soil on the Jingguan was blown away, and the white bones of the forest below were immediately revealed, and the so-called corpse mountain and blood sea were not just an adjective. The loyal souls of hundreds of thousands of martyrs are constantly screaming and summoning here.

In July 631, Li Shimin led a large army out of Shanhaiguan and entered the territory of Goguryeo, and immediately sent Sima Changsun Shi to destroy this Jingguan and bury the bones of the Sui soldiers one by one.

Goguryeo Mo Lizhi Yuan Gai Suwen, using Goguryeo's Rongliu King Gao Jianwu spent 16 years in the northeast from Fuyu City (later Jilin Siping), south to the sea to build a Great Wall of more than 1,000 miles as a barrier, as a barrier against the Tang Dynasty. The capital of the army is tense between the two countries.

At this time, Yuangai Suwen regarded himself as the leader of the Eastern Alliance, and decided to carry out a full-scale confrontation with the Tang Dynasty, and Yuangai Suwen also sent an envoy to Mobei, using "huge profits" to instigate the relationship between the Xue Yantuo Khanate and the Tang Dynasty, intending to contain the Tang Dynasty in the north. In terms of war preparations, on the one hand, it strengthened the "Great Wall" built in the Gao Jianwu period, and on the other hand, it gathered troops in the vast area between Liaodong and Yalushui and the Ganshan Mountains to build military bases, and vigorously strengthened the defensive forces of Liaodong City (later Liaoyang, Liaoning), Baiyan City, Fuyu City (later Jilin Siping), Xincheng, Gaimu City (later Fushun, Liaoning), Anshi City (later Gaizhou, northeast of Liaoning), Wugucheng (later Fengcheng, Liaoning), Beisha City (southwest of Pulandian, Liaoning) and other cities as the second line of defense, an attempt to blockade Don. The army attacked the routes and landed at the ports of attack by land and water, and carried out fortified walls in these places in an attempt to clear the wilderness in the Tang. When the army was short of food and salary, he took the opportunity to counterattack.

Li Shimin, Taizong of the Tang Dynasty, took Taichangqing Wei Ting as the feeding envoy, and Cui Renshi, the servant of the Ministry of Civil Affairs, was responsible for the transportation of grain and grass in the states of Yanzhao and Zhao; He ordered Xiao Rui, the servant of Shaoqing, to transport the grain and salary of the Central Plains states into the sea and store it in Wuhu Island to supply the needs of the water army.

Li Shimin issued an edict to the world, stating the five ways to win the Eastern Expedition to Goguryeo: "One is to attack the small with the big, the second is to fight against the rebellion with the smooth, the third is to control the chaos, the fourth is to wait for work with ease, and the fifth is to be happy and resentful." It is used to mobilize the people and strengthen the soldiers' belief in victory.

At this point, it can be said that everything is ready, and the horn of war has begun to sound.

Li Shimin knew that the Goguryeo State was no better than the Steppe Khanate, and as long as the army was strong in combat, everything could be solved. There were a large number of fortress-style castles in Goguryeo, and the battles were often fought later, and the pace was difficult.

Li Shimin appointed the general Li Tao as the vanguard, and sent troops to Liucheng (later Chaoyang, Liaoning), but on the other hand, he made a big noise and pretended to cross Liaoshui from Huaiyuan Town (northwest of Liaoyang, Liaoning in later generations), so Goguryeo put heavy troops on Huaiyuan.

Goguryeo overhauled the Great Wall on the border, and if the army marched head-on, then the only way to go was the famous swamp area in Liaodong, and Goguryeo was heavily fortified in this area, and Li Tao's vanguard was not many in number, and it was obviously not possible to meet head-on, so it could only be detoured.

Tang Dynasty. When the news of the army's crossing of Liaoshui reached Goguryeo, the whole country was shocked, and the cities were all closed and did not dare to attack.

A few days later, thousands of generals of Li Daozong, the deputy governor of Liaodong Province and the king of Jiangxia, arrived in Xincheng (later Shenyangdong, Liaoning), and Cao Sanliang, the commander of the capital, led more than ten horsemen to press the city gate, and the Goguryeo soldiers and civilians in the city were frightened and rioted and did not dare to resist.

Zhang Jian, the governor of Yingzhou, marched to Jian'an City (later southwest of Gaizhou, Liaoning) with Hu soldiers as the vanguard, defeating the Goguryeo soldiers who came to meet him on the way, and annihilating thousands of enemies.