In your textbook, there is a subsection that is entitled “The Mongols and Eurasian Integration.” Please consult it for further details.
Whenever there is a political entity that dominates a large area of land, trade and cultural integration are promoted. To understand how this is so, think of the Roman Empire. Before the Roman Empire (and after its fall) there was relatively little trade between the various parts of Europe. It was too dangerous to trade in places where there was no strong government to keep crime down. It was hard to trade among people with different legal systems. At the same time, there was little cultural integration. People did not have a great deal of contact with one another. They did not have a dominant culture from which they all borrowed. When Rome was at its height, all of these things did exist and therefore there was trade and cultural integration. The same is true of the Mongol Empire.
The Mongols dominated a huge area of Asia and even Eastern Europe. This was an area much larger than that ruled by Rome in past times. In addition, the Mongols took great pains to maintain order. This made trade much more possible than it had once been. Even as Mongol empires feuded with one another, they kept order and they did not inhibit trade among their empires. This meant that trade was much safer for merchants. Because of this, places that were as far apart as China and Western Europe came to have direct trade links for the first time.
This, of course, helped lead to cultural integration. Whenever there is trade, there is an exchange of ideas. This can happen through casual contact among traders and the people with whom they trade. It can also happen through things like missionary work (undertaken by Muslim and Christian missionaries during Mongol times) and resettlement efforts. The Mongols moved various peoples away from their homelands and put them in places where (the Mongols felt) they were needed or could be of help. All of these things led to mixing between cultures.
In these ways, the dominance of the Mongols helped bring about trade and cultural integration in Eurasia.