The Yuezhi, a pastoral confederation occupying the Gansu corridor, were defeated by the Xiongnu under Modu Chanyu around 176 BCE and again under his successor, who according to the Chinese sources killed their king and made his skull into a drinking vessel. The main body fled west into Dzungaria and the Ili valley, displacing the Sai (Saka) peoples in their turn; then, pushed again by the Wusun with Xiongnu backing, they moved south to the Syr Darya and by about 130 BCE crossed into Bactria, where they overthrew the Greco-Bactrian kingdom and eventually gave rise to the Kushan empire. A remnant, the 'Lesser Yuezhi', stayed behind and was absorbed. The episode is the best-documented ancient instance of a steppe state driving an entire people across a continent, and it is known almost entirely from Han Chinese records made because the Han were seeking the Yuezhi as allies against the Xiongnu; no numbers of any kind survive.
The Xiongnu confederation under Modu Chanyu and his successors defeated the Yuezhi of the Gansu corridor and drove them west, setting off a chain of displacements that ended with the Yuezhi conquest of Bactria
No count exists. The Shiji credits the Yuezhi with 100,000-200,000 archers, which if taken at face value would imply several hundred thousand people, but Han figures for steppe confederations are conventional and are not treated by historians as demographic data; there is no archaeological settlement basis for a pastoral population of this kind.
No death toll is recorded. Chinese sources note the killing of the Yuezhi king and the defeat of their armies but give no casualty figures, and losses during the long westward migration are entirely undocumented.
China, Afghanistan