Rodney Stark basically restates what is said in Robert Spencer's The Politically Incorrect Guide to Islam (and the Crusades), that Islam was not the haven of tolerance and enlightenment that it's advocates claim, and that the Crusades were wars of defence against Islamic aggression.
Tim points out that although Islamic forces had attacked Europe over a period of years, that was not mentioned in the call to arms by Pope Urban.
Stark Gets It WRONGThe Crusades were fought for a number of reasons, but the most important were religious motivations. As Tim says.
Stark's next section attempts to dismiss the idea that the Crusades were "unprovoked" and catalogues the Muslim atrocities and attacks on pilgrims that he claims were the "real" reasons the Crusades were launched. What is notable to any objective observer here is actually how little material he has to work with and how far back he has to go (mostly to the Eighth and Ninth Centuries) to find it. Of course, there were periodic pogroms against Christians in the Islamic world and sometimes Christian pilgrims were harassed. But if we imagine a situation where there were Muslim enclaves in western Europe or large groups of (heavily armed) Islamic pilgrims regularly journeying to, say, central Eleventh Century France, do we really suppose we would not see much the same thing happening?
That aside, these incidents and things like the destruction of the Church of the Holy Sepulchre in 1009 were the exceptions, not the rule. In addition, they do not feature in the reasons the Crusaders themselves gave for their expeditions in anything but the most peripheral way.
This last point can be extended into a key criticism of Stark's wider thesis as well. If the Crusades were, as he tries to argue, simply a reaction to Muslim encroachment into the European "homeland", why is it we do not see this reflected in any of the vast amount of material we have on the preaching of the First Crusade or any of the material we have on the motivations of the Crusaders? Did Pope Urban and the other instigators of the Crusades forget to mention this? And if this was the "true" motivation of the Crusaders, then launching a vastly expensive and highly dangerous 2500 mile long-distance military strike into Palestine, of all places, was an extremely weird way to carry it out. It is not like Jerusalem was the religious heartland of Islam (that was Arabia) or even its political centre (that was, if anything, Cairo) or even its intellectual centre (which was Baghdad).
If the real objective was to turn back the teeming tides of fanatical Muslim expansion from the gates of Europe, as Stark tries to make out, then the obvious target was far closer to home: in Spain. Stark even mentions, in passing, that one of Urban's papal predecessors, Alexander II, had already tried to stir the knights of Europe into joining the Spanish Christian kingdoms in attacking Muslim states in Spain back in 1063 , but the result was less than spectacular even by Stark's own fumbling admission:
The response was very modest. A small number of Frankish knights seem to have ventured into Spain and their participation may have helped recover more Muslim territory, but no significant battles were fought. (p. 46)So we are supposed to believe that, in 1063, a Papal call to meet the the supposedly pressing need to defend a beleaguered Europe from Islamic expansion could only muster up "a small number of Frankish knights", despite a promise of remission of sins for those who embarked, yet just 32 years later it sparked a mass movement, armies in the hundreds of thousands and wars that lasted over 200 years in a land 2500 miles from home? This simply makes zero sense.
Stark is clearly wrong. Plenty of solid scholarly work has been done in the last 60 years on the real motivations behind the Crusading ideal - millennial ideas about the coming apocalypse, idealised visions of Jerusalem not as a place but a mystical concept, the increasing alignment of knighthood with religious ideals, the outward expansion of western Europeans in all directions etc - but there is no evidence that they were ever seen as defensive wars against enemies encroaching on Europe, as the Spanish example clearly demonstrates.
As odd and unpalatable as it may be to modern people, the primary motivation of Crusaders seems to have been religious piety. It was usually a form of piety that modern observers find bizarre and was often one informed by myth and a weird idealism that we find hard to reconcile with modern Christianity or with any modern ideas at all, but the evidence is overwhelming that it was genuine and highly motivating.The Crusades were not fought to win riches on Earth, nor were they fought to convert Muslims to Christianity. For the most part the Crusaders went to war convinced that it was their spiritual duty to God.