Islam has always held a high regard for merchants. Muhammad himself was a merchant and many of the early evangelists of Islam were Arab traders themselves. A unique practice of these merchants was to practice direct trade, meaning that they traveled the entire length of a trade route instead of relying on local intermediary traders. As such, they were able to spread their religion far outside of their native Arabia. Their contacts with other merchants often led to conversions within the merchant class of their destinations and along their routes. This further stimulated the rapid spread of the religion. As such, it is not surprising that the spread of Islam from the seventh to the ninth centuries created a new vast trading zone.
By the end of the ninth century, Muslim merchants from Spain to Southeast Asia were trading with each other along a vast network of trade routes. Common ties of religion facilitated commercial relationships among many merchants and greased the wheels of trade.
Furthermore, the spread of Islamic empires, first under the Umayyads and then the Abbasids, united a vast swath of land under a single political force. These empires protected trade routes within their borders and encouraged merchants to sell goods throughout their domain and beyond. Under their protection, the Silk Road saw a resurgence of trade which connected the Islamic world with the far off markets of China and East Asia.
In short, it was the religion's high esteem of trade, the connections made between Muslim merchants, and the protections afforded by a large empire that led the creation of a single large trading zone. At the height of this trading network, goods from as far east as China were reaching ports all the way in Spain in the west, and products from Europe were being bought as far south as Ethiopia. All this was thanks to the vast trade networks of Muslim merchants.