Ancient Mongolian cave paiting
Xiongnu and Yuezhi
The first significant recorded appearance of nomads came late in the third century B.C., when the Chinese repelled an invasion of the Xiongnu (Hsiung-nu in Wade-Giles romanization) across the Huang He (Yellow River) from the Gobi. The Xiongnu were a nomadic people of uncertain origins. Their language is not known to modern scholars, but the people were probably similar in appearance and characteristics to the later Mongols. A Chinese army, which had adopted Xiongnu military technology--wearing trousers and using mounted archers with stirrups--pursued the Xiongnu across the Gobi in a ruthless punitive expedition. Fortification walls built by various Chinese warring states were connected to make a 2,300-kilometer Great Wall along the northern border, as a barrier to further nomadic inroads.
The Xiongnu temporarily abandoned their interest in China and turned their attention westward to the region of the Altai Mountains and Lake Balkash, inhabited by the Yuezhi (Yüeh-chih in Wade-Giles), an Indo-European-speaking nomadic people who had relocated from China's present-day Gansu Province as a result of their earlier defeat by the Xiongnu. Endemic warfare between these two nomadic peoples reached a climax in the latter part of the third century and the early decades of the second century B.C.; the Xiongnu were triumphant. The Yuezhi then migrated to the southwest where, early in the second century, they began to appear in the Oxus (the modern Amu Darya) Valley, to change the course of history in Bactria, Iran, and eventually India.
Meanwhile, the Xiongnu again raided northern China about 200 B.C., finding that the inadequately defended Great Wall was not a serious obstacle. By the middle of the second century B.C., they controlled all of northern and western China north of the Huang He. This
renewed threat led the Chinese to improve their defenses in the north, while building up and improving the army, particularly the cavalry, and while preparing long-range plans for an invasion of Mongolia.
Between 130 and 121 B.C., Chinese armies drove the Xiongnu back across the Great Wall, weakened their hold on Gansu Province as well as on what is now Nei Monggol Autonomous Region (Inner Mongolia), and finally pushed them north of the Gobi into central Mongolia. Following these victories, the Chinese expanded into the areas later known as Manchuria, the Korean Peninsula, and Inner Asia. The Xiongnu, once more turning their attention to the west and the southwest, raided deep into the Oxus Valley between 73 and 44 B.C. The descendants of the Yuezhi and their Chinese rulers, however, formed a common front against the Xiongnu and repelled them.
During the next century, as Chinese strength waned, border warfare between the Chinese and the Xiongnu was almost incessant. Gradually the nomads forced their way back into Gansu and the northern part of what is now China's Xinjiang-Uygur Autonomous Region. In about the middle of the first century A.D., a revitalized Eastern Han Dynasty (A.D. 25-220) slowly recovered these territories, driving the Xiongnu back into the Altai Mountains and the steppes north of the Gobi. During the late first century A.D., having reestablished the administrative control over southern China and northern Vietnam that had been lost briefly at beginning of this same century, the Eastern Han made a concerted effort to reassert dominance over Inner Asia. A Chinese army crossed the Pamir Mountains, conquered territories as far west as the Caspian Sea, defeated the Yuezhi Kushan Empire, and even sent an emissary in search of the eastern provinces of Rome.