“The First Crusade, the only militarily successful one of the six Christian invasions, took the Muslims by surprise. They had been fighting each other and had not expected an attack from Western Europe. Searching for explanations as to why they were being assaulted by a people from another part of the world, Muslims turned to mysticism and astrology, noting that Saturn was in Virgo.
Until then, lesser jihad had been the duty of a community but not necessarily all individuals, leaving a choice for those who did not want to fight. But during the Crusades, Muslim leaders declared that when Islam is attacked, jihad is the duty of every individual.
After the Crusades the interpretation of jihad became hard line. Ebu’s Su’ud wrote in the sixteenth century that peace with infidels was impossible and fighting should be permanent and unending.
The Crusades were about power, not relgion. And the Muslims understood this. Initially, they began looking for ties and seeking negotiations with the four new Medeterranean kindoms the Christians had established in the Middle East. But slowly they built their own war propaganda machine. Just as the Christians established a term for their enemy–the Saracens–the Muslims began calling all the Christian intruders al-frani, the Franks. Clerics began teaching that defeat at the hands of the Fanks was God’s punishment for their failure to carry out their religious duties. And one of the those duties was jihad. By reviving the culture of jihad the Saracens were able to build a counter-Crusade and drive out the Franks. It has happened throughout history: peoples who go to war tend to become mirror images of their enemy–another lesson.”
Mark Kurlansky, Nonviolence