The correct answer to this open question is the following.
During that time, classical empires fall, allowing the decentralization of many governments in Europe and China. The western Roman Empire collapsed, and the Byzantine Empire maintained Constantinople as an important trade hub, where people from afar regions gathered to exchange their goods.
So during the period of 600 to 1450 C.E., trade networks increased and included far away places such as the Arab Caliphates. Important trade routes such as the Silk Road, the Trans-Sahara trade, and the Indian Ocean trade maintained constant trade of precious metals such as gold and silver, fine silks from China, ivory from Africa, but also served to the spread of diseases such as the Bubonic plague.