The obvious response to this question is, "Well, what about them?" Violence committed in the name of other religions is logically unconnected to the question of whether Islam is violent. But, by mentioning the Crusades, the hope of the Islamic apologist is to draw attention away from Islamic violence and paint religions in general as morally equivalent.
In both the Western academia and media as well as in the Islamic world, the Crusades are viewed as wars of aggression fought by bloody-minded Christians against peaceful Muslims.
While the Crusades were certainly bloody, they are more accurately understood as a belated Western response to centuries of jihad than as an unprovoked, unilateral attack.
Muslim rule in the Holy Land began in the second half of the 7th century during the Arab wave of jihad with the conquests of Damascus and Jerusalem by the second "rightly-guided Caliph," Umar. After the initial bloody jihad, Christian and Jewish life there was tolerated within the strictures of the dhimma and the Muslim Arabs generally permitted Christians abroad to continue to make pilgrimage to their holy sites, a practice which proved lucrative for the Muslim state.
In the 11th century, the relatively benign Arab administration of the Holy Land was replaced with that of Seljuk Turks, due to civil war in the Islamic Empire. Throughout the latter half of the 11th century, the Turks waged war against the Christian Byzantine Empire and pushed it back from its strongholds in Antioch and Anatolia (now Turkey). In 1071, Byzantine forces suffered a crushing defeat at the Battle of Manzikert in what is now Eastern Turkey.
The Turks resumed the jihad in the Holy Land, abusing, robbing, enslaving, and killing Christians there and throughout Asia Minor. They threatened to cut off Christendom from its holiest site, the Church of the Holy Sepulchre in Jerusalem, rebuilt under Byzantine stewardship after it was destroyed by Caliph Al-Hakim bi-Amr Allah in 1009.
It was in this context of a renewed jihad in the Middle East that the Roman Pope, Urban II, issued a call in 1095 for Western Christians to come to the aid of their Eastern cousins (and seems to have harbored the hope of claiming Jerusalem for the Papacy after the Great Schism with Eastern Christianity in 1054).
This "armed pilgrimage," in which numerous civilians as well as soldiers took part, would eventually become known years later as the First Crusade.
The idea of a "crusade" as we now understand that term, i.e., a Christian "holy war," developed years later with the rise of such organizations as the Knights Templar that made "crusading" a way of life.
It worth noting that the most ardent Crusaders, the Franks, were exactly those who had faced jihad and razzias (raids) for centuries along the Franco-Spanish border and knew better than most the horrors to which Muslims subjected Christians.
At the time of the First Crusade, the populations of Asia Minor, Syria, and Palestine, though ruled by Muslims, were still overwhelmingly Christian. The "Crusading" campaigns of the Western Christian armies were justified at the time as a war liberating the Eastern Christians, whose population, lands, and culture had been devastated by centuries of jihad and dhimmitude. Conquering territory for God in the mode of jihad was an alien idea to Christianity and it should not be surprising that it (Christian holy war) eventually died out in the West and never gained ascendancy in the East.
Following the very bloody capture of Jerusalem in 1099 by the Latin armies and the establishment of the Crusader States in Edessa, Antioch, and Jerusalem, the Muslim and Christian forces fought a see-saw series of wars, in which both parties were guilty of the usual gamut of wartime immorality.
Over time, even with reinforcing Crusades waged from Europe, the Crusader States, strung out on precarious lines of communication, slowly succumbed to superior Muslim power.
In 1271, the last Christian citadel, Antioch, fell to the Muslims.
No longer having to divert forces to subdue the Christian beachhead on the Eastern Mediterranean, the Muslims regrouped for a 400-year-long jihad against Southern and Eastern Europe, which twice reached as far as Vienna before it was halted.
In geostrategic terms, the Crusades can be viewed as an attempt by the West to forestall its own destruction at the hands of Islamic jihad by carrying the fight to the enemy. It worked for a while.
Significantly, while the West has for some time now lamented the Crusades as mistaken, there has never been any mention from any serious Islamic authority of regret for the centuries and centuries of jihad and dhimmitude perpetrated against other societies. But this is hardly surprising: while religious violence contradicts the fundamentals of Christianity, religious violence is written into Islam's DNA.
Islam 101 was written by Gregory M. Davis, author of Religion of Peace?: Islam's War Against the World, and the producer/director of Islam: What the West Needs to Know.