Xiongnu
The Xiongnu () were a confederation of nomadic peoples who, according to ancient Chinese sources, inhabited the eastern Asian Steppe from the 3rd century BC to the late 1st century AD. Chinese sources report that Modu Chanyu, the supreme leader after 209 BC, founded the Xiongnu Empire.
Hexi Corridor
During the Han–Xiongnu War, Han China expelled the Xiongnu from the Hexi Corridor in 121 BCE and even drove them from Lop Nur when King Hunye surrendered to Huo Qubing in 121 BCE. The Han acquired a territory stretching from the Hexi Corridor to Lop Nur, thus cutting the Xiongnu off from their Qiang allies. Again, Han forces repelled a joint Xiongnu-Qiang invasion of this northwestern territory in 111 BCE. After 111 BCE, new outposts were established, four of them in the Hexi Corridor, namely Jiuquan, Zhangye, Dunhuang, and Guzang (Wuwei).
From roughly 115–60 BCE, Han forces fought the Xiongnu over control of the oasis city-states in the Tarim Basin. Han was eventually victorious and established the Protectorate of the Western Regions in 60 BCE, which dealt with the region's defense and foreign affairs.