All ethnic groups on Mongolian grassland live a nomadic life and are highly dependent on the natural environment. Why do you say that?
People on the grassland, whether in daily life or marching and fighting, mainly eat cattle and sheep and graze. Once encountering bad natural weather, such as snow and wind, the grassland will be deserted, cattle and sheep will lose forage, people will naturally lose their main source of livelihood, and the whole nation will soon come to the brink of life and death. If the weather is fine, the grassland vegetation is lush, the cattle and sheep are fat and the daily necessities are abundant, the population reproduction will be accelerated and the nation will grow. However, the carrying capacity of grassland to population is limited, which will objectively promote these nomadic peoples to expand foreign aggression and plunder.
According to the study of historical data, the cycle of extreme weather changes that affect grassland prosperity is generally 20 to 30 years. In other words, 20 to 30 years is a development cycle of Mongolian grassland nationalities. People on the grassland can't master this kind of cycle, so they envy the way of life of the farming people in the Central Plains. They can store grain in good years and spend it with "surplus grain" in poor years. From this point of view, it is easy to understand why nomadic minorities in the north always like to attack the Central Plains south.
However, this process of going south is always interrupted by climate change. Sometimes it seems that the attack in the south is smooth sailing, and it feels that we have to live a carefree life of drought and flood, and a snowstorm has disrupted their plans. The arrival of the snowstorm made the supply of soldiers a problem, and even Mongolian soldiers were in vain if they didn't have enough food. The Mongolian army had to retreat to the grassland and kill some war horses to make a living. After all, living is the right way. At that time, Emperor Wu of the Han Dynasty was able to levy and kill all the way, which should also have a certain relationship.
However, from 1200 to 1300, the grassland miraculously did not suffer from bad natural weather during this hundred years. The whole grassland is full of vitality and flocks of cattle and sheep. Grassland nomads are growing rapidly and population reproduction is accelerating. At this moment, the powerful Genghis Khan appeared, quickly unified all parts of the grassland, and formed a powerful political power and a brave army on the grassland. Mongolian tribes began to March south and expand to Europe.
What the whole world has seen is that the Mongolian nation mysteriously appeared in front of various civilizations, sweeping everything with the unique roughness of nomadic people, and a Mongolian empire across Europe and Asia was suddenly and rapidly established.