What brought about the revival of trade in the Middle Ages?

Agriculture started becoming a big part of their everyday life. Certain plants produced material to make clothing, and fruits and vegetables were a great source of food. Europe's techniques, along with other's production, it turned out to be a great source of "teamwork". One would produce clothing / food, as well as the others. They would each trade with one another, to make the process quite simple, yet fair, at the same time. This is actually what we use, to this day, considering we trade for money.