The Western Region, referring to today's Xinjiang Uygur Autonomous Region and the areas west to it, has long established close relation and exchange with the Central Plains.

At the beginning of the Western Han Dynasty (206BC-8AD), the Huns in the north were a serious menace, often harassing the frontiers of Han and looting vast quantity of riches. When Emperor Wu learned that a country called Dayuezhi was at enmity with the Huns, he decided to take this opportunity to enter into an alliance with Dayuezhi in the Western Regions so that the two countries could join hands in fighting against the Huns and keeping the frontiers eternally safe.

Emperor Wu sent Zhang Qianto the west to seek allies that could oppose the Nomads together. Zhang Qian traveled to many countries, obtained some information about the West that has never been obtained before and described China to each of these countries. In 119BC, Zhang Qian made his second trip to the west and the countries in the West sent ambassadors back. Finally, China was on friendly terms with these countries of the. These trips of Zhang Qian helped China to establish economic and cultural connections with the countries in the Western Region and enriched China's material richness.

During theHan Dynasty, Therefore, Emperor Wu issued an edict calling for volunteers who were courageous and capable enough to be Han emissaries in negotiating with Dayuezhi. At that time, nobody knew exactly where this country was, even less about how far away it was from Chang'an. Hence the apprehension was that this would be a trip of no return. There was, however, a young official named Zhang Qian, who thought it a meaningful undertaking and he became the first person to sign up. With Zhang Qian taking the lead, over 100 courageous young men immediately entered their names as well. Meanwhile, Tangyifu, an expatriate Hun living in Changan, had also expressed his willingness to join Zhang Qian's expedition in the search for Dayuezhi.

In the year of 138BC, Emperor Wu ordered Zhang Qian with over 100 brave men in his charge to leave Chang'an and try to establish contact with the country of Dayuezhi. However, hardly had they stepped across the boundary when they were taken prisoner by a troop of Hun cavalrymen. They had been held in captivity for ten years when Tangyifu and Zhang Qian, being kept in the same place, managed to escape when the Huns were off guard.

For many days on end, they kept on walking in a westerly direction despite tremendous hardships. Still they were not successful in their attempt to find the country of Dayuezhi. Instead, they found themselves in a country called Dayuan whose sovereign had heard that the Han Dynasty was powerful state and wanted very much to develop friendly relations with it. So the king was very happy when he saw Zhang Qian and he gave the envoy from the Han a warm reception. Later, he sent guides and interpreters to escort Zhang Qian and Tangyifu to a country called Kangju, via which they eventually reached Dayuezhi.