Yuezhi Migration (155 BCE)
According to the Han Chronicles the Yuezhi suffered another defeat around 155 BCE, against the Wusun, and fled south from the Ili river area, by-passed the urban civilization of the Dayuan in Ferghana, and re-settled north of the Oxus in modern-day Kazakhstan and Uzbekistan, definitively cutting Dayuan from contact with the Greco-Bactrian kingdom. The Yuezhi would further expand southward into Bactria around 125 BCE, and then going on to form the Kushan Empire in the 1st century CE.
Read more about this topic: Dayuan