 By the time of Modu's death in 174 BC, the Xiongnu had driven the Yuezhi from the Hexi Corridor, killing the Yuezhi king in the process and asserting their presence in the Western Regions.In 139 BCE the Emperor Wu of Han dispatched the former palace attendant Zhang Qian to form an alliance with the Yuezhi people in order to combat the Xiongnu.He was captured by the Xiongnu, and held prisoner for a decade.