Meanwhile, in 125 B.C., the famous Chang Ch’ien had returned.  He had been sent in 138 to conclude an alliance with the Yueeh-chih against the Hsiung-nu.  The Yueeh-chih had formerly been neighbours of the Hsiung-nu as far as the Ala Shan region, but owing to defeat by the Hsiung-nu their remnants had migrated to western Turkestan.  Chang Ch’ien had followed them.  Politically he had had no success, but he brought back accurate information about the countries in the far west, concerning which nothing had been known beyond the vague reports of merchants.  Now it was learnt whence the foreign goods came and whither the Chinese goods went.  Chang Ch’ien’s reports (which are one of the principal sources for the history of central Asia at that remote time) strengthened the desire to enter into direct and assured commercial relations with those distant countries.  The government evidently thought of getting this commerce into its own hands.  The way to do this was to impose “tribute” on the countries concerned.  The idea was that the missions bringing the annual “tribute” would be a sort of state bartering commissions.  The state laid under tribute must supply specified goods at its own cost, and received in return Chinese produce, the value of which was to be roughly equal to the “tribute”.  Thus Chang Ch’ien’s reports had the result that, after the first successes against the Hsiung-nu, there was increased interest in a central Asian policy.  The greatest military success were the campaigns of General Li Kuang-li to Ferghana in 104 and 102 B.C.  The result of the campaigns was to bring under tribute all the small states in the Tarim basin and some of the states of western Turkestan.  From now on not only foreign consumer goods came freely into China, but with them a great number of other things, notably plants such as grape, peach, pomegranate.

In 108 B.C. the western part of Korea was also conquered.  Korea was already an important transit region for the trade with Japan.  Thus this trade also came under the direct influence of the Chinese government.  Although this conquest represented a peril to the eastern flank of the Hsiung-nu, it did not by any means mean that they were conquered.  The Hsiung-nu while weakened evaded the Chinese pressure, but in 104 B.C. and again in 91 they inflicted defeats on the Chinese.  The Hsiung-nu were indirectly threatened by Chinese foreign policy, for the Chinese concluded an alliance with old enemies of the Hsiung-nu, the Wu-sun, in the north of the Tarim basin.  This made the Tarim basin secure for the Chinese, and threatened the Hsiung-nu with a new danger in their rear.  Finally the Chinese did all they could through intrigue, espionage, and sabotage to promote disunity and disorder within the Hsiung-nu, though it cannot be seen from the Chinese accounts how far the Chinese were responsible for the actual conflicts and the continual changes of shan-yue.  Hostilities against the Hsiung-nu continued incessantly, after the death of Wu Ti, under his successor, so that the Hsiung-nu were further weakened.  In consequence of this it was possible to rouse against them other tribes who until then had been dependent on them—­the Ting-ling in the north and the Wu-huan in the east.  The internal difficulties of the Hsiung-nu increased further.