Steppe, the Silk Road, and Han Wudi
The success of the unified bureaucratic form of government owes a great deal to military necessity: beginning in the third century BC, in circler to lend off incursions from the steppe, north China needed a government capable of deploying huge, well-trained fighting forces.
From long before Han times, China's contacts with the outside world had involved a combination of trade and military conflict. Chinese products like silk and lacquer-ware were superior to those of its neighbours, creating a demand for Chinese goods. Some neighbours had goods they could offer in exchange, such as timber, horses, sheep and cattle. But raiding was a common alternative to trade; non-Chinese groups who found that they could acquire the goods they wanted by force had less incentive to trade. Moreover, those normally willing to trade might turn to raiding when previously established trade relations were disrupted or when drought drove them to desperate measures. Defending against the raids of non-Chinese peoples had been a problem since Shang times, but with the rise of nomadism in the arid steppe north of China proper in mid Zhou, the severity of the problem was greatly exacerbated.
The Inner Asian steppe is a vast region of grasslands, mountains, and deserts, capable of supporting only a sparse population. In the best grasslands, such as those of modern Mongolia, rainfall is too light for grain to grow but animals can be pastured. Nomads of the steppe near China raised sheep, goats, camels, and horses, moving their camps north in summer and south in winter. Their skill as horsemen and hunters, especially their ability to shoot arrows while riding horseback, made them a potent military striking force. The typical social structure of the steppe nomads was tribal, with family and clan units held together through loyalty to chiefs selected for their military prowess. This structure could be exploited for efficient military mobilization when enough tribal units coalesced. The differences in the modes of living of farmers and herders led to sharp contrasts in their social values. For most of the imperial period, Chinese farmers looked on horse-riding pastoralists as a scourge, as pitiless gangs of bullies who preferred robbing to working for their living. The nomads, for their part, gloried in their military might and looked with scorn on farmers as weaklings incapable of defending themselves.
The first great confederation of nomadic tribes in Inner Asia was formed by the Xiongnu in the late third century BC. The First Emperor of Qin sent 100,000 troops against them in 213 BC, and his Great Wall was intended for defense against them. The early Han emperors tried conciliatory policies, wooing the Xiongnu leaders with generous gifts, including silk, rice, cash, and even imperial princesses as brides. Critics of these policies feared that they merely strengthened the enemy; and indeed, in 166 BC 140,000 horseman raided deep into China, reaching a point less than 100 miles from the capital.
Wudi took the offensive. He sent 300,000 troops far into Xiongnu territory in 133 BC. Subsequent expeditions, like those in 124, 123, and 119, often involved over 100,000 men. These campaigns were enormously expensive, requiring long supply lines and entailing great losses of men and horses. The gain was territory: regions north and west of the capital were acquired, cutting off the Xiongnu from the proto-Tibetan Qiang, whom they had subjugated. Four commanderies were established in Gansu, and more than a million people were dispatched to colonize this northwest region. At the same time Wudi sent troops into northern Korea to establish commanderies that would flank the Xiongnu on their eastern border.
Wudi turned his attention to Central Asia as well, in part to find allies, in part to improve the supply of horses for the army. In 139 BC he sent one of his officials, Zhang Qian, west in search of allies to fight against the Xiongnu. Captured and kept prisoner for ten years, Zhang eventually escaped and made his way to Bactria and Ferghana, returning in 126 BC. In 115 BC he set out on a second journey west. From his reports, the Chinese learned for the first time of other civilized states comparable to China that had developed independently of China. Ferghana, for instance, he described as 10,000 li (about 3,000 miles) due west of China, a land of fortified cities and dense population, that grew wheat and grapes for wine and had fine horses that sweated blood. He described Parthia in similar terms, but drew particular attention to its merchants and to its coins, made of silver and bearing the image of the king's face. Zhang Qian discovered that these regions were already importing Chinese products, especially silk. In 101 BC, after three years' effort, a Chinese army made its way beyond the Pamir Mountains to defeat Ferghana, seize large numbers of its excellent horses, and gain recognition of Chinese overlordship, thus obtaining control over the trade routes across Central Asia. The territorial reach of the Han state had been vastly extended.