to embrace Afghanistan with the frontier districts of India and Persia.[486] It is true that the Imperial authority in many of these regions was merely nominal:  when the Chinese conquered a tribe which claimed sovereignty over them they claimed sovereignty themselves.  But for the history of civilization, for the migration of art and ideas, even this nominal claim is important, for China was undoubtedly in touch with India, Bokhara and Persia.

But no sooner did these great vistas open, than new enemies appeared to bar the road.  The Tibetans descended into the Tarim basin and after defeating the Chinese in 670 held the Four Garrisons till 692, when the fortunes of war were reversed.  But the field was not left clear for China:  the power of the northern Turks revived, and Mohammedanism, then a new force but destined to ultimate triumph in politics and religion alike, appeared in the west.  The conquests of the Mohammedan general Qutayba (705-715) extended to Ferghana and he attacked Kashgar.  In the long reign of Hsuan Tsung China waged a double warfare against the Arabs and Tibetans.  For about thirty years (719-751) the struggle was successful.  Even Tabaristan is said to have acknowledged China’s suzerainty.  Her troops crossed the Hindu Kush and reached Gilgit.  But in 751 they sustained a crushing defeat near Tashkent.  The disaster was aggravated by the internal troubles of the Empire and it was long before Chinese authority recovered from the blow.[487] The Tibetans reaped the advantage.  Except in Turfan, they were the dominant power of the Tarim basin for a century, they took tribute from China and when it was refused sacked the capital, Chang-an (763).  It would appear however that for a time Chinese garrisons held out in Central Asia and Chinese officials exercised some authority, though they obtained no support from the Empire.[488] But although even late in the tenth century Khotan sent embassies to the Imperial Court, China gradually ceased to be a Central Asian power.  She made a treaty with the Tibetans (783) and an alliance with the Uigurs, who now came to the front and occupied Turfan, where there was a flourishing Uigur kingdom with Manichaeism as the state religion from about 750 to 843.  In that year the Kirghiz sacked Turfan and it is interesting to note that the Chinese who had hitherto tolerated Manichaeism as the religion of their allies, at once began to issue restrictive edicts against it.  But except in Turfan it does not appear that the power of the Uigurs was weakened.[489] In 860-817 they broke up Tibetan rule in the Tarim basin and formed a new kingdom of their own which apparently included Kashgar, Urumtsi and Kucha but not Khotan.  The prince of Kashgar embraced Islam about 945, but the conversion of Khotan and Turfan was later.  With this conversion the connection of the Tarim basin with the history of Buddhism naturally ceases, for it does not appear that the triumphal progress of Lamaism under Khubilai Khan affected these regions.