The Crusades
Since A.D. 638 Jerusalem had been controlled by local Muslim rulers. In 1009 the Muslims destroyed the Church of the Holy Sepulcher, Christ's tomb in Jerusalem, and began a series of attacks on Christian pilgrims. Hundreds were killed in 1064 when a party of 12,000 pilgrims was ambushed. Although the Church of the Holy Sepulcher was later restored to Christians, many Europeans wanted Jerusalem to be recaptured by a Christian army.
There were other pressures for a military crusade. The younger sons of noblemen hoped to win wealth and glory. The Roman Catholic Church thought a holy war would keep the violent knights usefully occupied. And the Church was having troubles of its own. When Urban II became Pope in 1088, the Church was divided: two men claimed to be Pope. Urban II hoped a crusade would help him gain an advantage over his rival. Some people believed that signs proved God wanted a Crusade. Stars had fallen from heaven and children had been born with extra limbs. One priest insisted that he had seen a crusader and a Saracen (Muslim) fighting in the Air.
At the End of the 11th century, Muslim armies attacked the Byzantine Empire. When the emperor sent to Italy for help, Urban II called for a crusade.