Xiongnu
Sinologist Edwin Pulleyblank argued that the Xiongnu were part of a Xirong group called Yiqu, who had lived in Shaanbei and had been influenced by China for centuries, before they were driven out by the Qin dynasty. Qin's campaign against the Xiongnu expanded Qin's territory at the expense of the Xiongnu. In 215 BC, Qin Shi Huang sent General Meng Tian to conquer the Xiongnu and drive them from the Ordos Loop, which he did later that year. After the catastrophic defeat at the hands of Meng Tian, the Xiongnu leader Touman was forced to flee far into the Mongolian Plateau. The Qin empire became a threat to the Xiongnu, which ultimately led to the reorganization of the many tribes into a confederacy.In 209 BC, three years before the founding of Han China, the Xiongnu were brought together in a powerful confederation under a new chanyu, Modu Chanyu. This new political unity transformed them into a more formidable state by enabling formation of larger armies and the ability to exercise better strategic coordination. The Xiongnu adopted many of the Chinese agriculture techniques such as slave labor for heavy labor, wore silk like the Chinese, and lived in Chinese-style homes. The reason for creating the confederation remains unclear. Suggestions include the need for a stronger state to deal with the Qin unification of China that resulted in a loss of the Ordos region at the hands of Meng Tian or the political crisis that overtook the Xiongnu in 215 BC when Qin armies evicted them from their pastures on the Yellow River.
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.