The Northward Migration of Pastoral Tribes and the Huns’ Southern Raids

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A well-known couplet from Tang poetry reads: "If only the flying general of Longcheng were here, the Hu horses would not be allowed to cross the Yinshan Mountains." In Chinese history, the Yinshan Mountains often marked a critical boundary between the agricultural Han Chinese in the Central Plains and the nomadic peoples to the north. The poet's wish for a steadfast defender like the legendary general Li Guang to guard this frontier reflects the recurring conflict between these two civilizations. Yet, history shows that the "Hu horses" frequently crossed the Yinshan Mountains. Why did these incursions occur?

Since the beginning of recorded history, conflict between the agricultural societies of the Central Plains and the nomadic peoples of the north has been a constant. The scope and intensity of these conflicts varied, but the geographic boundary often extended far beyond the Yinshan Mountains, encompassing regions from Liaodong in the east to Longxi and the Hexi Corridor in the west. While military leaders like the "Flying General" could defend key points, no individual could fully prevent such conflicts.

Traditionally, these struggles were attributed to the perceived barbarism, aggression, or backwardness of the nomadic peoples or, conversely, to the weakness and incompetence of the agricultural societies. However, this simplistic view overlooks the deeper dynamics at play.

Nomadic peoples depended on mobility for survival, living a life of "moving with water and grass." The Yellow River basin, once a shared homeland for both pastoral and agricultural peoples, gradually became dominated by the latter as their population grew and productivity improved. By the late Warring States period, nomads had been pushed north of the Great Walls built by the Qin, Zhao, and Yan states.

Under normal conditions, the movements of pastoral peoples were limited to seasonal or cyclical migrations. However, severe natural disasters—such as droughts, heavy snow, or locust infestations—or external pressures, like invasions, often forced them to migrate southward in search of better living conditions. Restricted migration left them with no choice but to fight for survival.

The nomads’ way of life, centered on horseback riding and archery, provided natural advantages in warfare. Their mobility and aggressiveness often overwhelmed agricultural societies. In addition to capturing land, they seized food, textiles, tools, women, and laborers from agricultural communities. These resources not only allowed them to survive crises but also improved their living standards, creating a cycle where raiding became an attractive and efficient means of acquiring wealth.

During the autumn, when horses were at their strongest and provisions for winter were needed, nomadic raids were most frequent and effective. The agricultural areas, lacking strong defenses, often fell victim to these incursions.

Over time, nomadic peoples developed a reliance on goods from agricultural societies, such as food, textiles, iron tools, and tea. These items became essential, yet the pastoral regions could not produce enough to meet their needs. For instance, though the Xiongnu began growing grain under Han influence, their output was limited, making supplies from the Central Plains vital.

Trade systems like the "mutual market" and "gate market" along the frontier were crucial for maintaining peace. However, the Central Plains rulers often misunderstood or deliberately manipulated the nomads' dependence on these goods, using it as leverage. This frequently led to conflict.

The vast differences in geography and economy between the two societies shaped their respective cultures. While each culture was adapted to its environment, the agricultural Han Chinese, situated in the fertile heart of East Asia, developed a sense of superiority. This perspective was codified in Confucian thought during the Spring and Autumn Period, which distinguished between Xia (the civilized agricultural peoples of the Central Plains) and Yi (the "barbaric" nomads and other non-Han groups). Such attitudes hindered mutual understanding and the establishment of peaceful relations.

The Han Dynasty faced significant challenges in its conflicts with the Xiongnu. The nomads, accustomed to harsher conditions, could thrive in both pastoral and agricultural areas, whereas the Han people struggled to adapt to the steppe environment. While the Xiongnu could expand their grazing lands southward, the Han could not extend agriculture into the arid north. This made the Yinshan Mountains the de facto northern boundary for agriculture, beyond which the Han could not sustainably expand.

Even when the Han achieved military victories against the Xiongnu, such as Emperor Wu's campaigns deep into the Mongolian Plateau, the results were often costly and unsustainable. For instance, while Emperor Wu's victories were celebrated, domestic opposition grew as resources were depleted. One official lamented: "We have abundant land, but farmers are conscripted as soldiers, leaving fields barren. Do we really need those dry and cold lands?"

When the Han Dynasty lacked the strength to confront the Xiongnu militarily, marriage alliances and trade agreements proved to be pragmatic solutions. Such policies allowed for periods of peace and stability, especially when the Xiongnu were relatively weak.

A turning point came during the reign of Emperor Xuan of Han. When the Xiongnu leader Huhanye Chanyu surrendered, Emperor Xuan treated him with dignity and generosity. Huhanye was given a status "above the princes" and received substantial material support. This policy established a precedent for peaceful coexistence. Emperor Yuan of Han later reinforced these policies, even recognizing a blood-oath covenant with the Xiongnu that symbolized equality and mutual respect.

As a result, the Han and the Xiongnu enjoyed an unprecedented 60 years of stability, during which border regions thrived, and conflicts diminished. The peace enabled prosperity on both sides, demonstrating that mutual respect and pragmatic diplomacy were more effective than prolonged warfare.

The question posed by the poet—how to "prevent the Hu horses from crossing the Yinshan Mountains"—cannot be answered simply by relying on a "Flying General." The incursions were driven by deeper economic, environmental, and cultural factors. True stability required not only military strength but also a nuanced understanding of the pastoral peoples’ needs and motivations. History shows that policies of coexistence, respect, and strategic trade were far more effective than force alone in fostering lasting peace between these two great civilizations.