The young Datang is destined to be full of disasters. Shortly after the pacification of the Western Regions, a new crisis arose in the southwestern border of the Tang Dynasty. A rapidly rising powerful force from the Qinghai-Tibet Plateau, Tibet, is becoming a new powerful threat to the Tang Dynasty.

In the 6th century, the Yalong tribe that arose in the area of Zedang and Qianjie on the Qinghai-Tibet Plateau has developed from a tribal alliance to a slave regime. Its leaders, Dabunesai and Nangri Ronzan, gradually extended their influence to the Lhasa River Valley.

Songtsen Gampo, the son of Nangri Nonzan, subdued the Qiang people Subi and Yangtong by force, and greatly increased his strength, moved the capital to Lhasa (Lhasa), formally established the Tubo Dynasty, and became the overlord of the Qinghai-Tibet Plateau from a small border country near the Brahmaputra River.

The expansion of Tibet inevitably encountered a strong enemy Tuyuhun who lived in Qinghai, and Tuyuhun was completely annexed to the Tang Dynasty after being destroyed by the famous general Li Jing in 637 AD. The ambitious Songtsen Gampo had naturally heard of the prestige of Tang Taizong Li Shimin's "Heavenly Khan" and the strength of the Tang Dynasty, so he tested the attitude and strength of the Tang Dynasty before turning the target of expansion to Tuyuhun.

In February 638 AD, Songtsen Gan sent an envoy to Tang, and Tang Taizong Li Shimin learned that there was such a country on the plateau and immediately sent an envoy to respond. However, Tang Taizong Li Shimin's response to Tibet was for diplomatic etiquette, and at the same time, his actions of harmony and affinity had a very strong purpose of governance, and Li Shimin naturally would not agree to the wishes of a new country that did not understand the strength situation.

Songtsen Gampo, who was refused, was furious, and in March 638 AD, he led the Qiang people who had already surrendered to the Qiang tribes, Subi and Yangtong, to raise troops to invade Tuyuhun, which had surrendered to the Tang Dynasty, and returned with a great victory. On the one hand, Tubo's move was to avenge the hatred of his relatives, and on the other hand, he also took the opportunity to attack the long-coveted wealthy Tuyuhun, who had already suffered a blow from the Tang Dynasty, and Tuyuhun was completely unable to resist the attack of Tubo.

After the victory, Songtsen Gampo was full of ambition, and took advantage of the victory to break through the Qiang tribes such as Dangxiang and Bailan, and even extorted more than 200,000 troops to invade the border city of Songzhou in the Tang Dynasty, defeated the defender Han Wei, and even threatened that "if you are not allowed to marry the princess, you should raise 50,000 soldiers, seize the Tang Kingdom, kill Er, and seize the princess."

The arrogance of Tubo made Tang Taizong Li Shimin furious, and he immediately reacted, sending Cheng Yanjin, the general manager of the Midao march, to lead Niu Jinda and Liu Lan to lead 50,000 cavalry to Songzhou.

At this time, Xia Xue was pregnant, due to the cold in the north, from October 638 AD, she moved to her original royal villa and royal garden in the southern angel special area to raise the fetus. The Tang Dynasty has a husband Li Shimin, of course Xia Xue doesn't have to worry; Angel companies also have their own cronies to manage, and there is basically no need to worry. Li Shimin was afraid of disturbing Xia Xue's fetal gas, so during Xia Xue's pregnancy, he would not tell Xia Xue about the big things in the court.

Tang Dynasty. After Niu Jinda, the general of the army's left military guard, arrived in Songzhou, he took advantage of the night to attack the Tubo military camp and "beheaded more than 1,000 ranks". Attacked by Don. Although Songtsen Gampo was very resentful after the military lesson, he had no choice but to retreat and return to the country.

The first time Tubo engaged in a large-scale battle with the Tang Dynasty, he was beaten so badly, Zampu was even more shocked when he heard about this, but he had to accept Niu Jinda's wisdom and bravery. Fan Zanpu then ordered the withdrawal of the army and sent an ambassador to apologize to Li Shimin, Taizong of the Tang Dynasty, and asked for intermarriage again, hoping to get Li Shimin's support.

After Li Shimin discussed with the ministers, Fang Xuanling and other old ministers felt that for the sake of peace on the Qinghai-Tibet border of the Tang Dynasty, which was cold and oxygen-deficient in the southwest, they suggested agreeing to this peace. After all, the altitude sickness, cold and lack of oxygen, bad weather, and strong ultraviolet rays on the Qinghai-Tibet Plateau are not adapted to most of the Central Plains Tang soldiers.

After deliberation, Li Shimin finally agreed to the ministers' proposal.

After Tang Fan saw each other's strength, they both changed their previous views on each other. Songtsen Gampo then sent an envoy to ask for peace, and at the same time sent the great minister Lu Dongzan to Chang'an to donate 5,000 taels of gold and hundreds of treasures as a dowry, and Li Shimin, Taizong of the Tang Dynasty, immediately agreed.

Li Shimin canonized the daughter of Li Daozong, the king of Jiangxia County, the cousin of Li Yuan, the ancestor of Tang Gaozu, as: Princess Wencheng, and ordered the envoys of Li Daozong, the king of Jiangxia County, to lead the troops to escort Princess Wencheng into Tibet and marry Tibet.

Songtsen Gampo was overjoyed and led his army and horses to greet him personally at the Baihai at the junction of Tang and Tibet. After seeing the princess, Zampu was extremely happy, and was very respectful to Li Daozong's son-in-law, and at the same time built a city in Heyuan to show his descendants. On the 15th day of the fourth month of the Tibetan calendar, Tubo welcomed his relatives and horses to Lhasa, and Tang Bohe personally reached this. Since then, the relationship between Tang and Tibet has entered a period of harmony.

After Princess Wencheng arrived in Tibet, a large number of advanced technologies of the Tang Dynasty were brought into Tibet. At that time, the farming technology of Tibet was quite backward, the fields were sparse, and the soil erosion was serious, and the farming tools and professionals brought by the princess taught the local people farming techniques, which greatly increased the yield of the land. The princesses and maids also taught the Tibetan women the techniques of weaving and embroidery. Of course, there are also various paper-making, metallurgical and wine-making techniques, which are essential life skills that have served Tibet far more than a princess.

A song was later circulated in Tibet:

"Princess Wencheng, the queen of the Tang Dynasty in Middle Earth,

There were 3,800 different kinds of food.

Lay a solid foundation for Tibet's grain.

Princess Wencheng, the queen of the Tang Dynasty from China,

5,500 craftsmen who brought different crafts,

It opened the door to the development of Tibetan craftsmanship.

Princess Wencheng, the queen of the Tang Dynasty from China,

5,500 different species of cattle were brought.

So that the cheese ghee of Tibet has been harvested every year. ”

The peaceful and pro-friendly policy of Li Shimin and his ministers to Tibet brought advanced Central Plains culture, a large number of technical personnel and materials to Tibet, greatly increased the productivity of Tibet, and accelerated the transformation of the Tibetan Empire from slavery to feudal centralization.

In March 642, after the death of Songtsen Gampo, the new Zampu (leader) of the rising Tibetan state on the Qinghai-Tibet Plateau: Mangsong Mangzan, young and ambitious, turned his back on his father Songtsen Gampo's diplomatic concept of harmonious coexistence with the Tang Dynasty, and began to invade the Tang border continuously.

Mangsong Mangzan took Gar Zannedob as his prime minister, and his younger brother was named Gar. Qinling led an army of 400,000 to the north, first taking Khotan and Shule, and then marching east to Qiuci, and then capturing several towns west of Yanqi, which shook the position of the Tang Dynasty in the Western Regions.

Li Shimin, Taizong of the Tang Dynasty, was furious when he heard the news, and took Xue Rengui, the general of the left guard, as the general of the march of the Luosao Road, and the general of the right guard, Ashina Daozhen, and the general of the left guard, Guo Beifeng, as his deputies, and led 50,000 troops to counterattack the Tubo army in order to recapture the four towns of Anxi.

On the ninth day of the fourth month, Xue Rengui led his army through Shanzhou (later Ledu, Qinghai) to Dafeichuan in Hunan, Qinghai. Xue Rengui knew that the Tubo army had many generals and a wide range of soldiers, and he waited for work at ease. The army must fight quickly to win the battle. Wuhai (later generations of Qinghai Kara Lake) is far away, the baggage chariots and horses are inconvenient to travel, and it is easy to lose fighters, so Guo Beifeng led 20,000 people to guard the baggage, grain and grass, so that it can be placed on the Dafei Ridge with danger, build fortifications, and make it a frontier position that can be attacked, retreated and defended.

Subsequently, Xue Rengui immediately led the main force and rushed lightly. The two armies met at the mouth of the river (later Maduo, Qinghai). The Tibetan army was caught off guard and was defeated, with many casualties and more than 10,000 cattle and sheep. Xue Rengui took advantage of the victory to occupy Wuhai City and waited for backup.

However, after Guo Zhifeng relied on the famous general Guo Xiaoke, he refused to accept Xue Rengui's control, led the rear team to advance without authorization, and failed to meet the coach in time. The Tubo army seized the fighter plane and invited more than 200,000 people to attack its troops, Guo Beifeng could not resist the enemy, and his baggage, grain and grass were lost.

Xue Rengui was forced to surrender to Dafeichuan.

Under the command of Qinling, the Tubo army forced the Tang Dynasty with an army of more than 400,000. Army decisive battle.