How did the spread of Islam create a new trading zone?
The spread of Islam created a new trading zone because it connected many areas of the world that had had no real connection in the past. In the hundred years or so after it was founded, Islam spread over an area reaching from Iberia in the west to Pakistan in the east. It then spread even further, getting into West Africa and into Central Asia. This allowed it to create a trading zone that covered almost an entire hemisphere.
When areas are controlled by one central government, trade among them becomes easier. This was true of Europe during the Roman Empire and it was true of much of Eurasia and parts of Africa under Islam. As Muslim rulers came to dominate these areas, trade between them was facilitated. There was no need to pass between many sometimes hostile countries. There was a common faith binding many of the merchants and causing them to have more trust in one another. These factors made it easier for trade to be conducted between places as far apart as China and Arabia.
The Muslims came to dominate a large area of the world. They revived the Silk Road through Central Asia. They sent seaborne traders around the Indian Ocean. They created banks and letters of credit and other things that made trade easier. Above all, they made it much easier and safer to travel from place to place within the area they dominated. This led to the creation of a huge new trading zone.