In the twelfth and thirteenth centuries, popes called for crusades against any groups they thought threatened
a. Catholicism.
b. Catholics living in northern Europe.
c. powerful kings in France and Spain.
d. the Mongols who lived in Asia.

The correct answer is any groups they thought threatened Catholicism.

The participants of the Fourth Crusade, financed by Venetian merchants, when they arrived in Constantinople, sacked the city and invaded the churches to remove the valuables.

The looting caused the weakening of Constantinople's trade and the strengthening of cities on the Italian peninsula, which began to monopolize the spice trade in the Mediterranean.

Although they did not fully achieve their religious objective, the Crusades promoted major changes across Europe, such as the reopening of the Mediterranean to European shipping and trade. This made it possible to intensify trade between the West and the East, which was largely interrupted by the Muslim expansion.

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b. ensure mutual protection from communism.

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