A realistic assessment of the Crusades, which are given in a number of articles, and the reasons why they were necessary can be found here. The calumny that the Crusades against Islam were either unnecessary or examples of Catholic Europe's bestial and blood-thirsty civilization, based on imperialism and plunder, is ruinously ignorant. The Crusades undoubtedly saved Europe, took the Holy War begun by Islam, to Muslim states, and bought Europe some 200 years in which it could further develop its already superior political-economy and military technology. There is no doubt that when viewing the evidence that Europe in the 7th century was far ahead of Muslim dominated areas; a competitive advantage which only accelerated between the 8th and 11th centuries. Archeology, Arab and Muslim records and the complex social, economic and political structures of Visigothic Spain, Italy and Gallic France, confirm this obvious fact.
There is no possibility that a 'Dark Age' continent would have had the wealth, the skill or the logistical technology to transport men to the Levant and fund their excessively expensive campaigns. The flow of specie was decidedly one-way, from Europe to the East. This is one reason amongst many including the lack of fighting men, discord and disunity, the dearth of emigration, and of course the eventual unity of the many Muslim statelets under one ruler, why the Crusades in toto, would be impermanent. But they certainly were not failures in the sense of not achieving important objectives. The change in mentality within Europe, and the self-confidence, premised on their superior civilisation was perhaps the most fundamental victory which the Crusades achieved. As a collective enterprise the Crusades awoke European exceptionalism and started Europe on its path towards world domination must to the benefit of the world. It takes a dull and fractured mind indeed to suggest that if Islam had conquered Europe and dominated Eur-Asian political-economy, that somehow we would all be 'better off'.
The crusades were in the main however a success on many levels. The latent power of Europe – when united – was plain to see. The crusades stimulated trade, industry and led directly to the destruction of feudalism. In the Knights Templar international trade and banking was pursued transforming the European economy; and in the Knights Hospitallers modern ideas of medicine and caring for the sick were introduced. Most importantly the crusades helped vivify the idea of Europe; of European civilisation and of European superiority. All of the energies and missionary zeal of the crusades lead to a more confident, more international and more prosperous Europe. It set the stage for the European domination of the world.
The crusades also forestalled of course the seemingly remorseless Muslim advance. No longer would Europe sit idly by and subject itself to the depraved depredations of the Turks and Muslims with their dhimmi-class system, onerous taxation of the infidel and swaggering arrogance that the moon cult should dominate the world. Finally the Europeans, however superficially, united and proved that Christian civilisation, however imperfect, was worth defending and able to project power across vast distances.
The crusades are a crucial turning point in history. They mark the beginning of the end of Muslim designs on Europe and world domination. They herald the awakening of the great European enlightenment and renaissance and they mark the first steps towards European world domination.
Indeed. They saved Europe.