How did the Han Dynasty open up China?

By the silk road, Han Dynasty open the trade with countries in the Middle East Asia.
By continuous wars, this dynasty established relationship with countries in Mongolia and Siberia.
By sea, it traded with East Asia and Southeast Asia. In many tombs in Asia, you can find relics of Han Dynasty. By all kinds of methods, Han Culture was spread to other countries and have an effect on culture of other countries.

Because of the silk road and the travel & trade it produced. previously, china had been isolated due to its geography, but with the silk road china could share cultures with the rest of the world.