Why did Zhang Qian travel the Silk Roads, and what places did he visit?

In fact, During the reign of the Emperor Wudi of the Han Dynasty (206 BC-220 AD), Zhang Qian was sent as a diplomatic envoy to the Western Regions at first. In 119 BC, Zhang Qian set off on his second journey to the Western Regions, in order to ally with Wusun (in Ili) Valley) against the Huns. He reached Wusun easily. Then he sent other envoys to Dawan, Kangju, Da Yuezhi, Anxi (Parthia, in now Iran), Juandu (present India), Yutian (Hetian) and other countries.