Why has China always attached importance to controlling the western regions since ancient times?

Historically, the central area ruled by the Central Plains dynasty has always included Shaanxi, while the western regions are closer to Shaanxi. From Shaanxi to the west, out of Jiayuguan, into what the ancients called the Western Regions. From now on, you can go directly to the western frontier. Although we have to cross the desert halfway, all the way is plain. Compared with the three strategic directions of east, south and north, marching from Shaanxi to the west is convenient for carrying materials, and the foreign population in the western region is small. Therefore, the military forces of the Central Plains Dynasty can successfully reach and control the Western Regions. In the Tang Dynasty, the cavalry of the Tang Dynasty used to move west of the Green Ridge for a long time, but in the late Xuanzong period of the Tang Dynasty, if they didn't advance, they would retreat and indulge themselves. Two traitors, Li and Yang, successively dominated the state affairs, which led to the decline of national strength, and 30,000 Tang Jun was defeated by150,000 Afghan troops. If Tang Xuanzong can maintain the spirit of the early years of Kaiyuan, perhaps Tang Jun will continue to expand to the west. With the strength of the Tang Dynasty at that time, it was not a dream for the forces to reach Europe. In that case, today's western region of China is not limited to the western region.

To the east of the Central Plains is the vast sea, with rough waves. It is very easy for the ancients to capsize when sailing, otherwise Japan would have become a province of China.

The Central Plains faces south, the weather is hot, the forest is dense, it is easy to get miasma, the mountains are high and the roads are long, it is difficult to supply materials, and there are many indigenous people who have always refused to accept Wang Hua. These are not conducive to large-scale military operations. Historically, Nanling was the dividing line between the Central Plains dynasty and the south. In ancient times, the south of Nanling (including Vietnam, Myanmar and other Southeast Asian countries) practiced the toast system. The chieftain is appointed by the central government and ruled by the chieftain, while the county system is centralized in the north of Nanling. This system continued until the Republic of China.

The north of the Central Plains, especially the Great Wall, is uninhabited and the weather is cold, which is not conducive to farming. The nomadic people living here, except livestock and meat, rely on trade with neighboring ethnic groups for other materials. If the Central Plains Dynasty exercised effective control over the north, it would have to station troops and emigrate. But the population was too small to immigrate. Crops cannot be planted without cold tolerance. From an economic point of view, controlling this area is not worth the loss, and the fiscal revenue here is far from military and political expenditures. Therefore, the ancient Central Plains dynasty had no interest in controlling the north and no effective policies. Otherwise, the Qing dynasty would not have allocated such a large piece of northern land to Russia.

In a word, with geographical, climatic, political, military, economic and other conditions, the territory of the ancient Central Plains Dynasty has expanded to the limit at that time. The ancient Central Plains dynasty occupied the best land in the world.