Although the route connecting the East and the West existed before Chinese Han Dynasty it was difficult to travel and the passage on this route was often interrupted by disputes and wars between different countries and nations. No security and safety were guaranteed.It was until the time of Zhang Qian that the route prospered mainly because of the effective measures adopted by the government of Chinese Han Dynasty when it established friendly relations with the countries beyond the Pamirs.
Chinese economy prospered in Han Dynasty and sericulture in particular was well developed. The economic boom stimulated the growth of population. The Han people began to expand southward. They crossed the Yangtze River and assimilated the aboriginal tribes during the process. They gradually moved into and developed the Pearl River Valley However, in the north, the migration of Han people stopped at the Great Wall and they could not go beyond as the Hun (Hsiung-nu) tribes often made inroad into the Han territory and presented a dangerous challenge to the Han people.
Hun was an ancient nomad nationality At that time, they occupied Mongolian Plateau, boasting of hundreds of thousands cavalries. They not only seized Dayuezhi and conquered dozens of small countries in the Western Regions, including Lolan, but also frequently attacked foreign traders and travelers in the region. It had seriously hindered the East-West traffic and transportation.
During its early period, Han Dynasty was no match for Hun. The army of Hun once even besieged Liu Bang, the founder of Han Dynasty.This humiliation was engraved deeply in the minds of the Han emperors,who vowed to revenge against the enemy. After more than 60 years of vigorous efforts, China became very strong militarily. When Wudi was on the throne of the Empire, the Han Dynasty entered a period of great prosperity with a powerful army. From the first day of his rule, Wudi was determined to take large-scale military action against Hun.