The Crusades were Christian military expeditions undertaken to recapture the Holy Land from the Muslims. Several crusading efforts were launched between 1095 AD and 1270 AD. The period of the Crusades was one of the most violent periods in the history of mankind.
Eastern aggression indirectly led to the start of the Crusades. After the death of Mohammed, Arab armies began successfully invading other nations. The Koran condemns aggressive acts of warfare, however a justification for the violations of Mohammed's principles was needed. Muslim jurist formed the concept of the jihad, or "holy war against unbelievers. Jihad is the duty of all Muslims" (Maalouf 282) . The jihad's objective was to conquer the rest of the non-Muslim world "so that the world could reflect the divine unity [of God]" (Armstrong 40).
Jerusalem had been under Muslim rule since the seventh century, but Christian pilgrimages to the Holy Land were not cut off until the eleventh century, when the Seljuk Turks began to interfere with Christian pilgrims.
For Christians, the name Jerusalem evoked visions of the end of time and of the heavenly city. The ideal of the Christian knight was to help rescue the Holy Land. Papal encouragement, the hope of eternal merit, and the offer of indulgences motivated thousands of Christians to enroll in the cause.
The starting point of the Crusades was on November 18, 1095, when Pope Urban II opened the Council of Clermont. On November 27, outside the French city of Clermont-Ferrand, the Pope made an important speech. He thought that Western Christendom should march to the rescue of the east and restore the peace. Urban appealed to the people at Clermont, detailing how
".... [the Muslim] has invaded the land of those Christians, has reduced the people with sword, rapine, and flame...