The construction of the navy army is of great significance to Li Xin. At least, when he was able to do it at the beginning, he had already begun to prepare for it. Although the inland water army is different from the ocean water army, at least, those soldiers who have trained in Shuofang are already completely familiar with the water nature. In this way, after several years of training in the Bohai area of Youzhou, there is no problem at all.

Attacking Pingzhou by sea was a shortcut for the Tang army, after all, it was impossible for the Yan army to build a fortress pass on the sea to defend against the Tang army.

With the start of the war, the territory of Yan Kingdom suddenly became a mess. Although the whole country had already been mentally prepared for the Tang Army's attack, because the Tang Army had not made any moves in the past year, everyone's hearts were relaxed.

So, Tang Jun suddenly appeared in front of him, and Yan Jun was stunned. Whether it was from Pingzhou or the local soldiers and horses in Qingzhou, the urgent documents from all over the country were sent to Murong Ping one after another.

Seeing this sudden news, Murong Ping panicked for a while, facing this kind of situation where flowers bloom everywhere and fights everywhere, where can he solve it. In the end, it was under the strong recommendation of Huangfu Zhen, Yue Juan and others that they ordered to recruit all the strong men in the country and prepare to enrich the front line.

In order to be able to resist the southward advance of the Tang army, Murong Ping arranged for Huangfu Zhen to be responsible for the defense along the Yellow River in the north after consideration. The defense of the mountainous area to the west was entrusted to Murong Zang, the king of Le'an.

As for himself, he remained in the city of Guanggu. Ostensibly, it means that he will sit in the center and be responsible for the central dispatch. But in fact, he had already begun to prepare slowly, preparing for a way to the east or south.

At this time, the strength of the Tang army to attack Yan had been roughly calculated. Not counting the soldiers and horses on the side of Youzhou, there are more than 100,000 troops from Sizhou and other places in the Central Plains. Although there are even more Yan troops in Qingzhou, no one is confident that they can stop the Tang army.

On April 15, the war had already begun for a few days. Chen Kang led an army of 30,000 troops from Yanzhou County to Juancheng County, all the way east, along the south bank of the Yellow River to attack Jibei and other places that were still under the control of the Yan army.

On the north bank of the Yellow River, there was an army of 30,000 led by Liu Xiaohai himself, who attacked from Guixiang County and Qinghe County, and wanted to cross the river and invade the northern kingdom of Jibei. Since Guixiang is only separated from Qinghe County and Jibei County by the Yellow River, once he crosses the river smoothly, he can directly enter the hinterland of Jibei County.

In that way, Jinyang Pass and other places used by Jibei County to resist the Tang army in the west were almost completely useless.

Liu Xiaohai and Chen Kang's actions had been discussed in advance, and the two worked closely together and relied on each other to attack.

On the other side, the attack in the area east of Pingyuan County was in charge of Shao Zisong, Shi Yue and others. Among them, Shao Zisong led an army of 30,000 from Leling County to the coastline, responsible for attacking Jinan County and Qi County on the south bank.

The area close to Pingyuan County was in charge of Shi Yue and others, and the 30,000 army wanted to cross the river and invade Jinan County in one fell swoop.

The focus of the war with Qingzhou is whether it can cross the Yellow River and enter the territory of Qingzhou. Otherwise, if we are never able to stand on the other side of the river, the war may not be fought in the end.

If you don't cross the river, you have to break through from the hilly terrain of Shandong in the western part of Qingzhou, where the terrain is steep, especially the defense system is relatively perfect, and it will not be easy to break through and advance smoothly from there.

Li Xin's idea is to solve the matter of Yan Guo as soon as possible, otherwise, once the time is delayed for too long, I am afraid that there will be some variables. Therefore, the main direction of the attack is still on the front line of the Yellow River.

A few days after the battle, from Hanoi, Luoyang and other places upstream, a group of warships went down the Yellow River and cut straight into the battlefield between Tang and Yan.

These days, the Tang army on the north bank wants to cross the river, but basically they have some small sampans and some ordinary fishing boats. Therefore, although the momentum of the offensive is large, the effect is not very good.

Therefore, although Huangfu Zhen, who was in charge of the first line of the Yellow River, was a little nervous, he was not completely unable to hold it. These ships arrived at night, and in the darkness of the night, they clung to the north shore and sailed down the river, and finally sailed into the territory of Guixiang County.

Here, Liu Xiaohai, who had been waiting for a long time, immediately ordered part of the army to get on the warship, and then quietly sailed into the area between Jibei County and Jinan County at night, and after forcibly landing there, he immediately launched an attack behind Jibei County.

Liu Xiaohai's attack caught Huangfu off guard. Because he didn't know at all that the Tang Army had already built a number of warships in Hanoi, Luoyang and other places. Otherwise, he should have been on guard against this a long time ago.

When the Tang army on the other side of the river was continuously transported to the Qingzhou territory by warships, Huangfu Zhen realized that the general trend had gone. Although he tried his best to organize soldiers and horses to resist, in the face of the morale of the Tang Army soldiers, and the fierce soldiers, it had no effect at all.

On 20 April, Liu Xiaohai, Shao Zisong, Shi Yue and other troops on the north bank of the Yellow River, with the help of warships, basically crossed the Yellow River and began to launch a full-scale attack on Qingzhou.

At this time, Huangfu Zhen had already led the army to retreat again and again, and directly withdrew from Jinan County. Originally, he wanted to stick to the defense of Jishui, but after seeing the tall war ships of the Tang Army, he knew that what he wanted was hopeless, so he simply gave up this unrealistic idea.

And Chen Kang, in the west of Jibei County, received Liu Xiaohai's help and support, and quickly broke through Jinyang Pass and directly entered the territory of Qingzhou.

At this point, the war between the Tang Dynasty and the Yan Kingdom in Qingzhou only lasted less than a month, and it had already begun to take a turn.

Hundreds of thousands of troops marched south with a thunderous momentum, quickly sweeping most of the Yan State's forces in Qingzhou, and countless counties and counties from all over the country surrendered to the wind. There are also more and more people who defect and surrender.

It only took less than ten days, and the entire Qingzhou territory had basically fallen into Li Xin's hands.

The imperial family of Yan in Guanggu City did not dare to stay since they heard that the Tang army had crossed the Yellow River. Murong Ping, Emperor Murong Wei and others packed their bags and fled all the way south, originally preparing to run to Jiangzuo in the south to save their lives.

After all, today, it seems that only Jiang Zuo can shelter them. However, their line dragged on too slowly, so that as soon as they ran out of Taishan County, they heard that the Tang army had already taken Juxian County and other places in the south, which was equivalent to directly cutting off their southern escape.