Nomadic empire
The Xiongnu were a confederation of nomadic tribes from Central Asia with a ruling class of unknown origin and other subjugated tribes. They lived on the Mongolian Plateau between the 3rd century BC and the 460s AD, their territories including modern day Mongolia, southern Siberia, western Manchuria, and the modern Chinese provinces of Inner Mongolia, Gansu, and Xinjiang. The Xiongnu was the first unified empire of nomadic peoples. Relations between early Chinese dynasties and the Xiongnu were complicated and included military conflict, exchanges of tribute and trade, and marriage treaties. When Emperor Qin Shihuang drove them away from the south of the Yellow River, he built the famous Great Wall to prevent the Xiongnu from coming back.
History of the eastern steppe
In 221 BC China was unified by the Qin dynasty and after a brief civil war, more permanently by the Han dynasty (206 BC – 220 AD). About 209 BC the steppe tribes were united by the Xiongnu. The two unifications were connected in that the nomads had to unite to protect themselves from the now-powerful Chinese and the Xiongnu ruler could strengthen himself with Chinese tribute. In the east, the Xiongnu conquered the Xianbei in Manchuria and in the west they drove the Wusun and Yuezhi westward. The Wusun soon disappeared, but the Yuezhi later had a great career as the Kushans of Afghanistan. In China, after about 75 years of internal consolidation and external tribute, Emperor Wu of Han adopted a forward policy. Zhang Qian went west (138-125 BC) and returned with the first good reports of the Western Regions. During the Han-Xiongnu Wars the southern Xiongnu in Inner Mongolia were subjugated and the northern Xiongnu were driven to northern Mongolia where they were broken up around 89 AD. The Han gained control of the Gansu Corridor and the Tarim Basin with some influence westward. This opened the Silk Road and led to the appearance of Chinese silk in the Roman Empire. As the Han declined the Tarim Basin experienced complex shifts of power between the Chinese, Xiongnu remnants and local rulers.
In the 19th century Western imperialism and industrialism began to impact eastern Asia. Steppe nomadism and many traditional Chinese institutions gradually became obsolete, both economically and militarily. In 1860 Russia annexed north and east Manchuria which soon acquired a Russian population. There was a massive migration of Han Chinese into Manchuria and Inner Mongolia which socially removed these areas from the steppe and attached them to China. When the Manchu dynasty fell in 1912 the Mongols claimed that they had been subject to the Manchus rather than China and were therefore now independent. This Russian-backed independence may have prevented Chinese immigration into the area. In recent decades there has been a significant Han migration into Xinjiang.