In 1095, Pope Urban II called for a war against the Muslim rulers of Jerusalem. This was the First Crusade. Over the next two centuries, Christian armies from Europe fought more crusades, but none was successful.
For centuries, Christian pilgrims had been visiting the Holy Land, where Jesus had lived and which had been ruled by Muslims since 637. The First Crusade happened because, by the 11th century, the region’s rulers were less sympathetic to Christian pilgrims.
Crusaders returned with apricots, lemons, rice, dyes, spices, perfume, soap, and glass mirrors. They also brought back a musical instrument, the ancestor of the modern guitar.