How did the migration of the Yuezhi lead to the Kushan empire?

The Yuezhi were originally nomadic people from northwestern China who migrated westward after being defeated by the Xiongnu in the 2nd century BCE. Upon reaching Bactria, they displaced the existing Greek rulers and divided the region into five distinct chiefdoms.12

The Kushan empire emerged from this migration when one of these five chieftains, the Guishuang (Kushans), rose to prominence. Approximately a century after the initial conquest of Bactria, the Kushan leader Kujula Kadphises unified these five chiefdoms under his own rule, establishing the Kushan dynasty. This unified kingdom subsequently expanded its influence across the Indian subcontinent, Afghanistan, and Central Asia, becoming a major power that facilitated the spread of Buddhism and fostered significant cultural and artistic exchange.12