The medieval Church enforced a strict and permanent economic blockade against Islamic powers.

Evidence

The canons and papal bulls attempted to impose a strict blockade of war materials; trade in arms, iron, wood for shipbuilding and sea-going craft was forbidden at all times, and trade in food and other useful matter was forbidden in time of war. Shipping was immobilised when a Crusade was projected and Christians were forbidden to serve in Muslim ships. After the fall of ‘Akka, all trade absolutely was prohibited, as though the war footing were permanent; and, from about the middle of the four- teenth century, the adoption of a system of special licences became an important source of revenue to the Holy See. — Norman Daniel, Islam and the West, 657