Why did the rich northeast become the "Great Northern Wilderness"?

Northeast China is rich in products and has a long history. For thousands of years, Xianbei, Qidan, Jurchen, Mongolia and other ethnic groups have created brilliant history from here. But by the end of the Qing Dynasty, the population of Northeast China was only over one million, which was a veritable Great Northern Wilderness. What is the root cause of this result? Northeast China has a long history. Thousands of years ago, Hongshan Culture's ancestors thrived here and stepped into the threshold of civilization. It is one of the cradles of China civilization. There are mainly four ethnic groups living in Northeast China, the area around Liaoning is inhabited by Han (Shang) people, and the central plain area is inhabited by foreigners, mainly farming. Su Shen's ancestors lived in the eastern forest region, and the Daxinganling region in the west was the living area of Xianbei people. The ancient climate was changeable, and it entered the Little Ice Age several times. The cold climate forced the ancestors of Northeast China to move south. In history, the five chaos in China, the nomads from Shanxi Province entered the Central Plains, the Mongolian cavalry went south, and the Manchu entered the customs, all because of the cold weather, which led to the loss of local population. On the other hand, the war has led to a population decline, and the population in Northeast China is already small. War leads to population decline and migration. In the ancient Central Plains, after years of war, a large number of people fled. When they win the war outside the customs, they will plunder the local population into the customs. This plunder went hand in hand with the war. For example, during the Three Kingdoms period, Cao Cao made an expedition to Wuhuan, and Sima Yi moved tens of thousands of people into Shanhaiguan after collecting gongsun's family in Liaodong. After Koguryo was destroyed in the Tang Dynasty, a large number of people moved to the mainland. Bohai Sea has one million registered permanent residence, so it is called Haidong Guo Sheng. After Yelubao flooded the Bohai Sea, a large number of people migrated, resulting in a decline in the local population. After the demise of the Jin Dynasty, the Xixia regime appeared in the northeast, and the population dropped sharply after the war. In the twenty years of Hongwu in Ming Dynasty, Northeast China returned to Chinese territory. After 300 years of operation, the northeast has a population of several million and a developed economy. There are dozens of developed cities such as Shenyang and Liaoyang. At the end of the Ming dynasty, the Qing dynasty rose, and decades of war caused a large loss of population. After the Qing army entered the Central Plains, a large number of Manchu people "entered the customs from the dragon" and entered the bustling place to enjoy family happiness. In addition, the Qing rulers banned * * * from entering the northeast, which made many cities in the northeast waste and decline, leading to "beating the roe deer with sticks and throwing fish and pheasants into the rice cooker." "The great northern wilderness. Considering the climate, the northeast is cold and the grain output is low, so it is difficult to feed a large population. Therefore, the population in the late Qing Dynasty exceeded 400 million, while the population in the Northeast was only over one million. At the end of the Qing Dynasty, Russia was worried about the Northeast, forcing the Qing Dynasty to lift the ban, and a large number of surplus farmers from Hebei and Shandong flooded into the Northeast, setting off a wave of marching into the Northeast. During this period, cold-resistant and drought-resistant crops such as sweet potato, corn, potato and sorghum were popularized. Cotton cloth has become the main material for ordinary people since the Ming Dynasty. Cotton filler can resist the long and cold weather in Northeast China, which provides convenience for immigrants. At the end of the Qing Dynasty, the Middle East Railway opened the Guanzhong Railway, which provided a lot of employment opportunities with convenient transportation. Many conditions enabled Guanzhong immigrants to enter the Northeast by land and water, and more than 30 million immigrants settled in the Northeast, completing the largest migration in human history. After the founding of New China,100000 troops entered the northeast reclamation land and built many farms. The development of Daqing Oilfield has been supported by all parts of the country. After several generations' efforts, the vast and sparsely populated northern wilderness in the past, cities have mushroomed, farmland is contiguous, and villages are everywhere. Northeast China has become an important industrial base in China and a big granary with an annual output of hundreds of millions of kilograms of commodity grain.