At its height, about 150 - 250 CE, Kushan rule stretched from Tajikistan to the Caspian Sea to Afghanistan and down into the Ganges river valley. The empire was created by Tocharians from modern Xinjiang. At their height, they had diplomatic contacts with Rome, Sassanian Persia and China.
The name Kushan derives from the Chinese term, traditionally transliterated Guishang, that described a branch of the Yuezhi (q.v.)— a loose confederation of Indo-European peoples speaking versions of the Indo-European Tocharian language. They were the easternmost Indo-Europeans, who had been living in the arid grasslands of the Karim Basin, until they were driven west by another group, the Xiongnu, in 176–160 BCE.
The Yuezhi reached Hellenized Bactria (northernmost Afghanistan and Uzbekistan) around 135 B.C. In the following century, charismatic leaders welded the group into a tighter confederation. Gradually wresting control of the area from the Parthian tribes, the Yuezhi expanded south into the region traditionally known as Gandhara (the Pathan areas now shared between Pakistan and Afghanistan) and established a capital near present-day Kabul. They adapted the Greek alphabet, whichthey encountered in Bactria, to suit their own language and soon began minting coinage, the first in India.
The rule of Kanishka, the third Kushan emperor, who flourished from the late first to the early/mid-second century A.D., was administered from two capitals: Purushapura (now Peshawar in northern Pakistan) and Mathura in northern India. The rule of the Kushans linked the seagoing trade of the Indian Ocean with the commerce of the Silk Road, through the long-civilized Indus Valley. At the height of the dynasty, Kushan loosely oversaw a territory that extended to the Aral Sea through present-day Uzbekistan, Afghanistan, and Pakistan into northern India. The loose unity and comparative peace of such a vast expanse encouraged long-distance trade, brought Chinese silks to Rome, created strings of flourishing urban centers, and eventually encouraged the expansion of Buddhism into Central Asia.
The art and culture of Gandhara, at the crossroads of the Kushan hegemony, are the best known expressions of Kushan influences to Westerners.