Why did Shanxi become a buffer region between Chinese farmers and northern nomads?

Shanxi’s role as a buffer region between sedentary Chinese farmers to the south and east and pastoral nomads to the north and west was established during the Han dynasty (206 bce–220 ce).1

This strategic function was primarily defined by the province's geography. Shanxi serves as a gateway to the fertile plains of Hebei and Henan, making it a critical defensive position for protecting the agricultural heartland of China from incursions originating from the Mongolian and Central Asian steppes. Because of this location, the province historically functioned as a major avenue for military expeditions and trade, necessitating its role as a protective barrier.21