How did social and political changes in western europe during the 1100s lead to an increase in trade

There are several changes, but I believe that the end of the barbarian invasions, the increasing population, development of cities, the possibility of using the agriculture surpluses (grains) in trades exchanges, and finally, the Crusades are the better.

Explanation:

The transition of the X century for the XI century was a moment of changes in Europe. When the barbarian invasions finally ended, the medieval world knew a period of peace, safety, and development. With the end of wars and the retreat of diseases, the population increased. This considerable number of people created a demand for food which stimulated the creation of new agriculture techniques. Trade exchanges begin to be common between the villas that were rising here and there. Soon, many villas turn into big cities, surrounded by high walls. Finally, when Jerusalem was taken by the Muslims, the Crusades support the development of the trade with the East.

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