Stark is a sociologist who delights in digging up evidence undermining the conventional wisdom on issues of history and faith; which is what he does provocatively in God's Battalions.
Provocatively, because it is undisputed in the school education system and general culture that the Crusades were `a bad thing', that the Muslims were on the side of the angels, that the `Christians' were primitive thugs, and that all the current woes of the West's relationship with the Middle-East are merely the inevitable outworking of this earlier, unfortunate phase of our history. Stark refutes all these givens.
A significant problem for us in considering the Crusades is that we are dealing with a culture that is in pretty much every respect alien to us. It is hard to imagine ourselves into a world where everyone was deeply religious, yet at the same time often deeply immoral. To step back into medieval Europe would be at least as culturally disorienting for us as going to live amongst the Taliban today. Our cultural grid is radically different from that of our Crusading forbears.
The greatest tragedy of the Crusades is perhaps that those taking part truly believed that by doing so they were atoning for their sins and earning salvation. A clear understanding of salvation by grace through faith would have avoided a lot of grief... But this erroneous theology did produce some colourful characters: "Thorvald was a renowned Viking who had converted to Christianity... He undertook a pilgrimage in 990 seeking to atone for having killed two poets who had mocked his faith and another man who had criticized his preaching." I feel a certain empathy with Thorvald..!
Stark takes a broadsword to the assumptions we have about this period of history. He refutes the accepted wisdom that Muslims were tolerant of non-Muslims in the lands they conquered. He argues that the accomplishments of Muslim culture were actually the accomplishments of Christians and Jews (the dhimmi) living under Islamic rule, and that the Muslim population itself was culturally backward. (For example, the Dome of the Rock mosque in Jerusalem was built by Byzantine architects and craftsmen rather than Muslims.) He accepts Crusader claims on their own terms - that Muslims were the aggressors, who had invaded Christian lands, and oppressed the Christians over whom they ruled. He states that "Muslim memories and anger about the Crusades are a twentieth-century creation" in response to British and French imperialism after World War I and the creation of the state of Israel after World War II.
The fact that "the total number of books translated into Arabic during the 1,000 years since the age of Caliph Al-Ma'moun (a ninth-century Arab ruler who was a patron of cultural interaction between Arab, Persian, and Greek scholars) to this day is less than those translated in Spain in one year" has been oft quoted and Stark claims that "the inability of Muslims to keep up with the West occurred because Muslim or Arab culture was largely an illusion resting on a complex mix of dhimmi cultures, and as such, it was easily lost and always vulnerable to being repressed as heretical. Hence when in the fourteenth century Muslims in the East stamped out nearly all religious nonconformity, Muslim backwardness came to the fore."
Stark argues that the military successes of the Crusaders were also due to Muslim backwardness. For example, the Muslim navy was composed of ships that were copies of the boats of Christians, and were crewed by mercenaries from the West - this inevitably put them at a disadvantage against the more up-to-date craft of the Crusaders, and their more motivated crews.
A recurring theme in Stark's romp through the Crusading centuries is the tension that existed between Eastern and Western Christianity. Again and again the Byzantines, who had requested help from the West in order to resist the encroaching Muslims, betrayed and undermined the Crusader armies. That the Crusaders plundered Constantinople is often quoted as an example of the brutality and idiocy of the period, but reading Stark's arguments it becomes much more understandable why this event occurred.
Stark concludes his book pithily,
"The thrust of the preceding chapters can be summarized very briefly. The Crusades were not unprovoked. They were not the first round of European colonialism. They were not conducted for land, loot, or converts. The crusaders were not barbarians who victimized the cultivated Muslims. They sincerely believed that they served in God's battalions."
This conclusion will probably jar against everything you have ever been told about the Crusades, and if for no reason other than that this book is worth a read.