Why did Emperor Wu of the Han Dynasty send people to the Western Regions?

In order to find out this problem, today I finally began to turn over the history books that have been sealed for many years:

During the Western Han Dynasty, Yumenguan, Yangguan, the east of Congling and the north and south of Tianshan Mountains in Gansu were called the Western Regions. Later, it developed to the west of Qinling Mountains, and Central Asia and beyond, all of which were called the Western Regions.

In the early years of the Western Han Dynasty, because the Han Dynasty was often harassed by the Huns, the Huns suddenly became fierce bandits, haunting the grasslands. The people far away in the border were harassed, and the monarch of the Western Han Dynasty had a headache. Later, Zhang Qian was sent to the Western Regions as an envoy. Originally, I wanted to form an alliance with the Da Yue family, unite to destroy the Huns, and make the border peaceful. At that time, Zhang Qian met the Huns when he passed the Green Ridge with more than 100 people, and was imprisoned for several years.

At that time, Zhang Qian finally arrived at Dayue in 10. In ancient times, traffic was scarce and information update was slow. Zhang Qian repeatedly failed to persuade Da Yue, and finally had to return to Chang 'an. On the way to the meeting, I met Xiongnu again, but I survived every time. When he was sent to Yuezhi for the second time, Yuezhi was already on the handrail, but Zhang Qian was obsessed with the characteristics and customs of the western regions. Finally, I applied to start the Silk Road.

Later, his deputy envoy also came to Chang 'an with the ministers of Dawan and Kangju. Zhang Qian's two missions to the Western Regions did not achieve the direct goal, but they strengthened the ties between the Han Dynasty and other countries in the Western Regions and opened the way to the Western Regions.