In 176 BC, the Yuezhi were driven from Tarim Besin to westward by the Xiongnu, a fierce people of Magnolia.
The Yuezhi under the leadership of the Kushanas came down from Central Asia and swept away all earlier dynasties of the Northwest in a great campaign of conquest. They established an empire which extended from Central Asia right down to the eastern Gangetic basin.
In Bactria, they conquered the Scythians and the local Indo-Greek kingdoms, the last remnants of Alexander the Great's invasion force that had failed to take India.
From this central location, the Kushan Empire became a wealthy trading hub between the peoples of Han China, Sassanid Persia and the Roman Empire.
Roman gold and Chinese silk changed hands in the Kushan Empire, at a very tidy profit for the middle-men.