When the Eastern Han Dynasty was still relatively strong, the annexed states under its control were very different from those of the Wei and Jin dynasties.

To put it simply, the annexation of states in the Eastern Han Dynasty included most of today's Shanxi Province, the northern half of Shaanxi Province (called Shangjun in the Eastern Han Dynasty, including today's Yan'an, Yulin and other places) and part of Inner Mongolia (called Shuofang, Wuyuan, and Yunzhong Counties in the Eastern Han Dynasty, including today's Baotou, Bayannur, Ordos, Hohhot and other places). In the Eastern Han Dynasty, except for the interior of Shanxi Province, most of the other places were inhabited by Han and Hungarians. (Therefore, there are documents that Lu Bu, who was born in Wuyuan County, has Hun blood)

During the Wei and Jin dynasties, on the one hand, China fell into civil war, its national strength declined, and its control over the border areas quickly weakened. On the one hand, the steppe peoples moved southward and encroached on a lot of the inherent land of the annexed states. And the Southern Xiongnu, who had been grazing on these lands, were powerless to resist...... Therefore, the annexation of states in the Wei and Jin dynasties was basically similar to the modern Shanxi Province.

The two major pieces that were dismembered, the northern part of Shaanxi, in this era were mainly dominated by the Qiang people, there were also many Xianbei people here, and the Xiongnu also retained a certain territory. Therefore, when historians mark this period of this territory, they all use the words 'Qianghu mixed residence'. The essence of Inner Mongolia was all occupied by the Xianbei people.

Because the Hetao was too fat and the strategic location was too important, soon after taking Guanzhong, Guan Yi sent Wenyang to recover the Hetao. Therefore, now Ji Han has an enclave in the northwest of the former Eastern Han Dynasty: Wuyuan County. Jiang Wei's starting base is here.

And the upper county, which links Chang'an and Wuyuan County, Ji Han does not have the ability to restore it at this time. It's just that a straight road was built through Upper County. Guan Da Sima did not ask too much of the many tribes grazing on this land: you sell us the wool, and usually help me keep the straight road smooth and safe. You can do whatever you want to do with other things.

Go east from Shangjun and cross the Yellow River, which is Xihe County. This is the base camp of the Xiongnu after moving south. The Xiongnu Shan Yuting was set up here. Further east from the West River is the core county of Bingzhou: Taiyuan County.

To the north of Taiyuan County is Yanmen County. However, at this time, the Yanmen County of the Jin Kingdom was much smaller than the Yanmen County of the Eastern Han Dynasty, at least the places north of the Great Wall were basically occupied by the Xianbei people.

To the south of Taiyuan County is Shangdang County (Shanxi high-ranking official city). The South Gate Huguan in Bingzhou, and the current Dongdaemun Jingcheng Pass (Niangzi Pass was only available in the late Sui and early Tang Dynasties), are all in Shangdang County. The core of the so-called merger state shape is actually Shangdang County. Only by taking Shangdang County can we truly have the geographical advantage of overlooking the Central Plains.

However, according to the traditional route of marching troops, if Guan Yi's 150,000 wanted to enter Bingzhou, he would not actually go to Shangjun to cross the Yellow River and enter Bingzhou. Instead, they crossed the river at the place of Pubanjin in Fengyi County, first going east into Hedong County in Sizhou, and then going north into Bingzhou.

The reason why we want to march along this route is, of course, also due to the special geographical environment of Shanxi.

Shanxi, mountains and rivers in the surface. On its west side, it is separated from Shaanxi Province by the Yellow River. Crossing the Yellow River from northern Shaanxi, while entering Shanxi Province, it also entered a large mountain longitudinal from north to south: Luliang Mountain.

The east side of Shanxi: Taihang Mountain. North side: Wutai Mountain, Heng Mountain. South side: Zhongtiao Mountain, Wangwu Mountain. It can be said that the whole of Shanxi Province, like Sichuan, is surrounded by mountains on all sides.

However, although there are many hills in the Sichuan Basin, there are basically no large mountain ranges, and there are many plains in the basin. In the interior of this province surrounded by mountains on all sides, there are also such things as the Zhoushan Mountain, the Taiyue Mountain, the Yunzhong Mountain and part of the Loess Plateau. The interior of Shanxi Province as a whole is not a large basin as a whole. Rather, it is because various mountains and plateaus are divided into six large basins and more than ten small basins. These six basins are the essence of ancient Shanxi.

In the case of Guan Yi's departure from Chang'an, he wanted to march into Bingzhou and take the core of Shangdang County, a beautiful place in the world. The best route is to go north from Chang'an, take Pubanjin, and enter Hedong County in Sizhou, Jin State, which is in the Yuncheng Basin of modern Shanxi Province. Not only is the terrain flat here, but also the Laishui flowing from east to west can be used, which is convenient for transporting military rations and other logistical materials.

After taking Hedong County, the Han army could continue to march in a northeasterly direction: northeast of the Yuncheng Basin, is the Linfen Basin. The terrain is also very flat, and there are large rivers such as Fenshui to help transport rations. After taking here, in the north, along the Fenshui to the north is the Taiyuan Basin, where the Fenshui and the coastal river valleys can be used, and the march is also very comfortable. To the east, although there is a large area of the Loess Plateau, there is no huge mountain range to block it - over this plateau, it is the Changzhi Basin - this era is called Shangdang County.

In short, the process of conquering and annexing states from west to east is basically this. After taking Taiyuan County and Shangdang County, the annexation of the state will be counted.

Of course, due to the terrain, the best route to march from west to east and merge with the state is almost always unique. So, how can people like Du Pre and Wang Jun not see this?

From November 271, after it was determined that Jihan would begin a national conscription. Wang Jun set out from Taiyuan County and personally led 10,000 elites to be stationed in Puban City, Hedong County, Sizhou. At the same time of constantly reinforcing Puban City, it also requisitioned local people, taking Puban City as the midpoint, along the east bank of the Yellow River, to the south, to the north, and constantly building small dock forts - in short, Shaanxi wants to enter Shanxi, and the flattest section is only such a section. I'll just guard this section - if you have the ability, you can go over Luliang Mountain!

In December, after the recruitment of the Jin State was effective, Du Pre directly added 40,000 soldiers and 10,000 people to Wang Jun.

At present, the distribution of Jin forces on the Bingzhou front (including Hedong County in Sizhou) is as follows:

Wang Jun, the former enemy commander, sat in Puban City, east of the river, with 50,000 troops.

The commander of the front army, Du Pre, sat in Shangdang County and had 70,000 troops.

The sixth son of Sima Fu, the king of Taiyuan, Sima Gui, and his son Sima Hao sat in Taiyuan County, with 20,000 troops.

In Du Yu's view, the key point to resist Jihan's strategy of merging states is not in the state itself, but in Puban City. Therefore, he deployed heavy troops in Hedong County, Sizhou. According to Du Xuan's idea, it was absolutely impossible for Ji Han to forcibly cross the Yellow River and seize the beach in this season, and then attack Puban City on the shallow river beach, without paying more than 50,000 people.

Of course, Ji Han has had many military miracles over the years, so Pusaka City is not without the possibility of being captured. Therefore, Du Yu did not press all his troops to Hedong County.

In Du Xuan's plan, it would be nothing if Ji Han took Puban City with heavy casualties or a miracle of war: Wang Jun's troops would have to retreat.

After Guan Yi took Puban, it was unlikely that he would attack Taiyuan when Shangdang had heavy troops stationed in it - without Shangdang County, it would be meaningless to take Taiyuan County. Therefore, in Du Pre's inference, if Guan Yi takes Pusaka, he will definitely take the eastern front to take the party.

But is this place so easy to take? Although the two most important checkpoints of the Shangdang, one faces south and the other faces east, there is no restriction on Guan Yi from the west. But there is a large loess plateau between Hedong County and Shangdang County, the key is that Hedong County belongs to Sizhou, which is very close to Luoyang! In addition to being the most fortified city in the world, Luoyang also has 80,000 national standing troops and 20,000 princely guards.

So, what should you Guan Zifeng do after crossing the Yellow River and taking Pusaka? Go directly to Luoyang? Then the troops on my side of the party will hit you in the back. Are you going to hit the party? Okay, I'll step back, stretch your supply line, and fight you here at Huguan - your back will be attacked by the Luoyang Chinese army.

This is Du Pre's strategy of merging states: first use Pusaka City to block the opponent's crossing of the river and consume its vital forces. Then put the Han army into two huge pincers composed of the Bingzhou Army and the Luoyang Central Army. It can be said that due to the natural terrain advantage, if Guan Yi's 150,000 troops really crossed the Yellow River and entered Puban, one careless would be the annihilation of the entire army.

On June 20, 272, Guan Yi led 150,000 Han soldiers to Pubanjin.

In this season, the Yellow River has a huge amount of water and a very fast flow rate. On the bank of the Yellow River, looking at the roaring Yellow River, and on the other side of the Yellow River, Puban City is full of people waving flags and shadows. The soldiers above and below Ji Han all turned pale and complained bitterly.

The only one with a normal expression was Guan Yi: "Order, the whole army is camped on the west bank of the Yellow River, we won't leave!" ”