Final answer:
In 138 BCE, Emperor Wudi of the Han Dynasty sent Zhang Qian on a mission to form an alliance with the Yuezhi against the Xiongnu; after being detained for ten years, Zhang returned with valuable insights that broadened China's trade and political ties.
Step-by-step explanation:
In 138 BCE, Han Dynasty emperor Wudi sent Zhang Qian on a diplomatic mission with dual purposes. Initially, Zhang Qian was sent to forge an alliance with the Yuezhi, a nomadic group, as a strategic move against the Xiongnu confederation, with whom the Han had a tense relationship despite an existing mutual recognition agreement. However, Zhang Qian was captured by the Xiongnu and detained for a decade. During his captivity, he learned much about Central Asia. Upon his escape, he managed to continue his journey, visiting regions including present-day Kyrgyzstan, Uzbekistan, and Afghanistan, and eventually returned to the Han court with valuable information on those distant lands and potential markets for Chinese silk. This intelligence proved significant for the Han Dynasty's future foreign policy and trade expansions.
Zhang Qian’s mission marked the beginning of the Silk Road trade network, and his exploration broadly opened direct political and trading relationships between China and the Central Asian kingdoms, eventually leading toward contact with the Roman Empire. Emperor Wudi's far-reaching diplomatic and military strategies, which included sending out troops and establishing commanderies beyond China's traditional borders, significantly expanded the influence of the Han Dynasty.