The Kushan Empire was a syncretic empire, formed by the Yuezhi, in the Bactrian territories in the early 1st century. It spread to encompass much of Afghanistan, and then the northern parts of the Indian subcontinent at least as far as Saketa and Sarnath near Varanasi (Benares), where inscriptions have been found dating to the era of the Kushan Emperor Kanishka the Great. Emperor Kanishka was a great patron of Buddhism. He played an important role in the establishment of Buddhism in the Indian subcontinent and its spread to Central Asia and China.
The Kushans were one of five branches of the Yuezhi confederation, a possibly Iranian or Tocharian,
]Indo-European nomadic people who migrated from Gansu and settled in ancient Bactria.The Kushans possibly used the Greek language initially for administrative purposes, but soon began to use Bactrian language. Kanishka sent his armies north of the Karakoram mountains. A direct road from Gandhara to China remained under Kushan control for more than a century, encouraging travel across the Karakoram and facilitating the spread of Mahayana Buddhism to China.
The Kushan dynasty had diplomatic contacts with the Roman Empire, Sasanian Persia, the Aksumite Empire and the Han dynasty of China. While much philosophy, art, and science was created within its borders, the only textual record of the empire's history today comes from inscriptions and accounts in other languages, particularly Chinese.
The Kushan empire fragmented into semi-independent kingdoms in the 3rd century AD, which fell to the Sasanians invading from the west, establishing the Kushano-Sasanian Kingdom in the areas of Sogdiana, Bactria and Gandhara. In the 4th century, the Guptas, an Indian dynasty also pressed from the east. The last of the Kushan and Kushano-Sasanian kingdoms were eventually overwhelmed by invaders from the north, known as the Kidarites, and then the Hepthalites.