It was under the Emperor Wu-ti (140-87 B.C.) of the Han dynasty that the Chinese first penetrated into the Tarim basin. They had heard that the Hsiung-nu, of whose growing power they were afraid, had driven the Yüeh-chih westwards and they therefore despatched an envoy named Chang Ch'ien in the hope of inducing the Yüeh-chih to co-operate with them against the common enemy. Chang Ch'ien made two adventurous expeditions, and visited the Yüeh-chih in their new home somewhere on the Oxus. His mission failed to attain its immediate political object but indirectly had important results, for it revealed to China that the nations on the Oxus were in touch with India on one hand and with the more mysterious west on the other. Henceforth it was her aim to keep open the trade route leading westwards from the extremity of the modern Kansu province to Kashgar, Khotan and the countries with which those cities communicated. Far from wishing to isolate herself or exclude foreigners, her chief desire was to keep the road to the west open, and although there were times when the flood of Buddhism which swept along this road alarmed the more conservative classes, yet for many centuries everything that came in the way of merchandize, art, literature, and religion was eagerly received. The chief hindrance to this intercourse was the hostility of the wild tribes who pillaged caravans and blocked the route, and throughout the whole stretch of recorded history the Chinese used the same method to weaken them and keep the door open, namely to create or utilize a quarrel between two tribes. The Empire allied itself with one in order to crush the second and that being done, proceeded to deal with its former ally.
Dated records beginning with the year 98 B.C. testify to the presence of a Chinese garrison near the modern Tun-huang[483]. But at the beginning of the Christian era the Empire was convulsed by internal rebellion and ceased to have influence or interest in Central Asia. With the restoration of order things took another turn. The reign of the Emperor Ming-ti is the traditional date for the introduction of Buddhism and it also witnessed the victorious campaigns of the famous general and adventurer Pan Ch'ao. He conquered Khotan and Kashgar and victoriously repulsed the attacks of the Kushans or Yüeh-chih who were interested in these regions and endeavoured to stop his progress. The Chinese annals do not give the name of their king but it must have been Kanishka if he came to the throne in 78. I confess however that this silence makes it difficult for me to accept 78-123 A.D. as the period of Kanishka's reign, for he must have been a monarch of some celebrity and if the Chinese had come into victorious contact with him, would not their historians have mentioned it? It seems to me more probable that he reigned before or after Pan Ch'ao's career in Central Asia which lasted from A.D. 73-102. With the end of that career Chinese activity ceased for some time and perhaps the Kushans conquered Kashgar and Khotan early in the second century. Neither the degenerate Han dynasty nor the stormy Three Kingdoms could grapple with distant political problems and during the fourth, fifth and sixth centuries northern China was divided among Tartar states, short-lived and mutually hostile. The Empire ceased to be a political power in the Tarim basin but intercourse with Central Asia and in particular the influx of Buddhism increased, and there was also a return wave of Chinese influence westwards. Meanwhile two tribes, the Hephthalites (or White Huns) and the Turks[484], successively became masters of Central Asia and founded states sometimes called Empires--that is to say they overran vast tracts within which they took tribute without establishing any definite constitution or frontiers.