Why do you say that without the sixteen states of Youyun, the Central Plains Dynasty can only go down forever?

When it comes to this issue, we can first look at which of the sixteen states are, and try to briefly analyze why the sixteen states are so important to the Central Plains from the aspects of geography, strategic position, economy and national defense resources, so that without these sixteen states, the Central Plains Dynasty can only generalize.

"Quiet" is today's Beijing, "Cloud" is today's Datong, and sixteen states of quiet clouds generally include today's Hebei, northwestern Shanxi and Beijing. Since ancient times, Tianjin has been the main barrier for the Central Plains Dynasty to stop the northern nomads from invading south. The sixteen states are Youzhou, Ruzhou, Tanzhou, Jizhou, Zhuozhou, Yingzhou, Xinzhou, Guangxi, Wuzhou, Yuzhou, Yingzhou, Atlas, Shuozhou and Yunzhou. It is roughly a large area of land in Beijing, Tianjin, northern Hebei and northwestern Shanxi.

? Look at the map. It's in the Great Wall. The terrain is condescending, easy to defend but difficult to attack. Recovering Yanyun is equivalent to having a solid line of defense against the enemy. Part of the reason why the Northern Song Dynasty always wanted to recover Yanyun was that Song Taizong was defeated by Gaolianghe during the Northern Expedition and fled in a donkey cart. Later the emperor wanted to avenge himself. Song Shenzong also made a decree that anyone who answered Yan Yun should be crowned king, so that many generals were vying for this fat meat. In fact, a large part of the reason is that Yanyun is a battleground for military strategists.

At that time, sixteen counties, on the Great Wall, were equivalent to nomads attacking the bridgehead of the Central Plains, and they could fight wherever they wanted in the Central Plains. No breakthrough. In addition, Sixteen States was also a fairly rich region at that time, with many advanced technologies and cultures in the Central Plains.

? Sixteen counties are a dangerous place, easy to defend but difficult to attack. The loss of sixteen States and the northern barrier directly led to the naked exposure of the Central Plains to the northern minorities, and the decline of the Song Dynasty was also closely related to it.

Speaking of national defense resources, this is also one of the biggest shortcomings in the Song Dynasty. China's geographical position, in the Yellow River valley, is the Great Plains. Once out of the Great Wall, it is a great plain. Therefore, to fight in the north, there must be cavalry. And China in the north to deal with the enemy of the Great Wall, more depends on cavalry. Horses needed by cavalry are produced in only two places in China. One is in the northeast and the other is in the northwest. First, the so-called Jibei wasteland, which is today's hot spot. First, Gansu-Lianghetao area. You have to be in a cold place to keep a good horse. You can't raise horses one by one. You have to raise horses in groups in a long ravine with beautiful grass, sweet spring and open land in order to make a long-distance pursuit for cavalry. The geographical conditions of sixteen counties are just suitable for large-scale horse breeding. Once the Sixteen States fell, it meant that the Central Plains dynasty lost the initiative in the plain war, and it could only be a corner of peace and was passively beaten.