Crusades were seen by many in the West as a religious act, caring the banner of Christianity against the non-Christian Muslim world. There was also a strong political component. There were in fact several Crusades keeping this fighting going for two centuries. The Muslims were at first defeated and then managed to eject the Crusaders and start to rebuild the Muslim world. While some in the West might use the term "crusade" in a non-religious manner today, to Muslims the word continues to conjure images of an invasion by the West specifically as an expression of bigotry against Islam.
The Western powers fought the Crusades against the Muslims for several reasons, and the religious element was only one of those reasons. The Muslim world at the time was divided into factions, and Muslim Spain had started to go its own way in the eighth century. Much of the Muslim world was by then under attack from the Seljuk Turks, but the Muslims were also in control of the Holy Lands, the seat of Christianity. In the eleventh century, European Christians set out on the Crusades to recapture the Holy lands, especially the city of Jerusalem. The Crusaders saw an opportunity because of the divisions within the Muslim world at that time. The Christian world also suffered its own divisions, such as the splitting off of the Byzantine Empire because of the disintegration of the Holy Roman Empire. This left the Greeks in power in the East, while the remains of the Roman world were in power in the West. The Church now had eastern and western factions.
Vernon O. Egger in the Introduction to his book about the era states,
The phrase Muslim world, as used in this book, refers to regions ruled by Muslim-dominated governments, as well as areas in which the Muslim population is a majority or an influential minority. For several decades in the seventh century, the Muslim world was coterminous with the region often referred to today as the Middle East, but it soon expanded far beyond that heartland. By the tenth century, many of the most important cultural developments in the Muslim world were taking place outside the Middle East. The size of the Muslim world has alternately expanded and contracted over time, and we will be concerned to see how and why that has happened.
By the eleventh century, the world of Islam was in decay. Economic decline was caused by the extravagance and lack of organization at the center. The weakness of the Empire was seen in a series of attacks by internal and external barbarians on all sides. The Turks were making inroads. The Seljuqs were Sunni Muslims, and they conquered Baghdad and became the new rulers of the Empire, relying heavily in administration on Persians and on the Persian bureaucracy. Social upheavals were inevitable, and trade withered and declined. There was a reorganization of the economy and in religious life. The Seljuq Empire eventually broke up into a series of smaller succession states. The Crusades brought Christian forces into conflict with the Spanish Muslims and Turks. Trade was affected. In the East, a new threat to Islam developed in the form of Jenghiz Khan. The Mongol invaders were heathens and showed no interest in Islam. In the middle of the thirteenth century the Mamluk Sultanate emerged to rule Egypt and Syria until 1517.
By the end of the tenth century, an Islamic world had come into existence that was united by a common religious culture expressed in the Arabic language and that was joined by human links forged by trade, migration, and pilgrimage. This world was divided into three broad areas, each with its own centers of power, and with three rulers claiming the title of caliph, in Baghdad, Cairo, and Cordoba. These and other political changes did not destroy the cultural unity of the Islamic world, which grew deeper as more and more of the population became Muslims and the faith of Islam articulated itself into systems of thought and institutions.
In the period of expansion and growth, the majority of peoples coming under the sway of Islam accepted the new religion either because it had a simplicity that appealed to them or because they were taking the way of least resistance and accepting the faith in order to claim equality of status with the new rulers. Arabs and non-Arabs were thrown together in a new society which was completely different from what had existed before. Many of the civilizations that came into contact with Islam were ancient civilizations, and often the Muslims did not make any radical changes in these new territories. Indeed, these extant civilizations had an influence on the Islamic world so that soon there was not the unity there had originally been. Instead there were new sects within Islam This tension both divided and served to reinvigorate the Muslim world with an infusion of new ideas and with encouragement for inquiry into a variety of fields. The Islamic world in its developmental and expansionist phase during the Golden Age was open to ideas from outside just as it disseminated ideas to the outside world through open contacts. In the Islam of the time, scientific inquiries were encouraged as much as philosophic inquiries, and this had a basis in the Quran as that work persistently invites the faithful to examine the created world in order to appreciate the greatness and the power of God. Scientific knowledge of nature, the stars, the heavens, the earth, the flora, and the fauna therefore only reinforces the faith, and there was also a literature of mirabilia, or the miracles of nature, halfway between scientific observation and religious contemplation. The people of Islam developed mathematics, including algebra, geometry, trigonometry, and arithmetic; astronomy; botany; pharmacology; zoology; geography; physiognomy; and psychosomatics to a high degree, and the West was the beneficiary of this knowledge from the twelfth century on. The growth of this and other fields of learning within Islam, however, came to a halt as Islam retreated.
Against the Reconquista in Spain, the Crusades in Palestine, and the Turkish and Mongol hordes in Iran and Iraq, Muslims believed they needed an orthodox, dogmatic, and rigid Islam to rally around. The retreat that followed was more a withdrawal from active participation and from contact with certain outside influences as a way of protecting the Islamic world. While there is clear evidence that the scientific thought of Islam contributed to the development of science elsewhere in the world, it is also true that scientific investigations seem to have stopped, or at least to have faltered, with the end of the golden Age. Islam itself did not benefit from its knowledge as much as did the European Renaissance, for instance, and the Scientific Revolution, while dependent on the foundation of Islamic learning, occurred outside the Islamic world, raising the question of why.
This retreat followed the majority of the Crusades and such other threats as the sacking of Baghdad by the Mongol marauder Halaku Khan in 1258 and similar losses in the Islamic world. These invasions came at a time when Islamic civilization was already in decline, and these external factors cannot be cited as the sole cause of the retreat. Indeed, most of the marauders in time settled down and became Muslims themselves. There were elements internal to the society which played a very important role in arresting its economic, political, and intellectual evolution. The first part of the problem was the weakness of autonomous institutions like cities and trade guilds because of the fact that the caliphate in Islam was not determined by institutionalized, well-defined procedures which would assure continuity of policy of encourage alternate centers of power. Another element was the different way religion entered the sphere of politics in Islam…