There's nothing a person says that more serves better to convinces me of their ignorance than when they use the "C" word. They use it as if it was a magical talisman that would make us crumble to the ground and eagerly convert to whatever twaddle they're peddling. People who believe the Crusades were somehow "bad" inevitably are completely and unforgivably ignorant of both Christian and Moslem histories, let alone the infamous and barbaric treatment of Christians under invading Moslem armies in Spain, Portugal and France between AD 711-1492.
The Crusades weren't started by Christians or the Church. Instead, they were slow, measured, moral, reasonable and rational responses to violent and unchecked Islamic invasion and colonization. If anything, the Crusades were supremely holy when compared to the egomaniacal, selfish and hate-filled wars started by atheists between the 18th and 21st centuries. The Crusades were started to protect innocent Christians from being killed. Atheists start wars because they hate, are jealous and because they desire power. To be clear, every war started by Moslems has been, indeed a religious-inspired carnage but this doesn't mean that every other war was religious in nature. Islam teaches that war is perfectly in keeping with Allah's capricious and vindictive nature.
By the time the Crusades had started in AD 1099, invading Moslem armies had slaughtered countless thousands of Christians in the Levant, the Middle East, Saudi Arabia, Spain, Portugal, France and Italy. A full 90% of Christian territory had been unjustly invaded and annexed. And under the lash of their "peaceful" Moslems overlords, Christians were enslaved, raped, forced to pay the extortionist tax known as the jizya, forced to convert to their peaceful religion, summarily executed for no other reason than they were Christians in a formerly Christian country unjustly taken over by evil Moslems. In fact, Moslems had controlled Spain and Portugal for 400 years before the Catholic Church came to realize that Moslems not only wanted Christian lands and wealth, but also wanted to enslave and destroy Christian souls.
To reinforce this point, let us consider the behavior of Moslems in Spain two centuries prior to the First Crusade. The 9th-century Christian Martyrs of Cordoba died as a result of a nonviolent campaign during the early Carolingian period in Cordoba, Spain, the seat of power of the Moslem invading forces. At the time of their martyrdom, most of the Iberian Peninsula was under Moslem control for the previous century. As a response to outrageous human rights violations, a group of Christians living in Cordoba initiated a pacifistic movement that proved beyond a shadow of a doubt that Islam has never been a "religion of peace."
Despite wide-scale administrative efforts on the part of the invading Moslem armies of forcing Christian Spaniards and Portuguese to convert to Islam but by threats of violence and the jizya, only the very poor were swayed—simply because they couldn't afford the exorbitant taxes imposed on them and they were fearful for the safety of their children being sold into sexual slavery by Moslems.
The evil perpetrated by Moslems spurred a Christian revival within Moslem-occupied Spain and Portugal. However, by AD 850, the Cordoba-based government met this Christian resistance with a horrific pogrom but, despite the terror unleashed against the Christians, very few converted to Islam. In April, AD 850, Moslems arrested a Catholic priest named Perfectus and accused him of insulting Mohammed and subsequently murdered him. St. Perfectus' murder resulted not in violent riots but rather in widespread displays of Christian non-violence and noncooperation. Christians took to the main plazas of Cordoba and denounced Islam and its founder Mohammed pointing out that the religion wasn't based in peacefulness. Many of these Christians, clerics, monks, nuns, lay people, Moslem apostates (repentant Christians who had converted to Islam and then reverted back to Christianity) were arrested and tortured but the nonviolent protests continued through to AD 852. It was in this same year when local invading ruler Emir Abd al-Rahman died. Emir Mohammed I (AD 852-56) succeeded him but the Christian pacifists gained momentum. Church leaders, faced with the out-of-control nonviolent revolt in Cordoba and by a fiercely violent one in Toledo, called a council at Cordoba to end the confrontation. In December 852 the council honored the fallen as martyrs but called on Christians to avoiding any more confrontations that would result in their deaths. Church historian Eulogius of Cordova composed his Memoriale sanctorum (Memorial of the Saints) and Alvarus the first part of the Indiculus luminosus (The Remarkable List).
In June 853, five additional Christians came forward to proclaim their faith. The emir was overwhelmed by the Christians' faith and threatened to massacre all Christian men and to sell Christian women into prostitution. Though he backed down from this initial threat, the emir purged all Christians from the government, imposed severe taxes (i.e., jizya) destroyed churches, monasteries and schools and launched a massive forced conversion of the Christian populace to Islam. In AD 854, however, Alvarus published the second part of his Indiculus luminosus which condemned Mohammed and equated him with the Antichrist of the Apocalypse (1 Jn 2:18-22, 4:3, 2 Jn 1:7, Rev 16:13, 19:20, 20:10). In AD 855, Christians again spoke out against the Islamic invaders in the public squares and before the magistrates, urging Moslems to convert to Christianity. For this, they were martyred out of hand, but this didn't stem the flood of Christians eager to witness to the Faith. Eulogius was executed in AD 859 and with his death came the end of the martyrdom movement. However, the deaths of thousands of Christians served to reinvigorate the Crusaders fighting in the Reconquista in the unoccupied lands of Spain and Portugal.
Thus Christians, natives of their own country, chose to bless and pray for their persecutors, peacefully and nonviolently as the Master Himself taught us:
But I tell you who hear Me: Love your enemies, do good to those who hate you, bless those who curse you and pray for those who mistreat you. If anyone hits you on one cheek, let him hit the other one too; if someone takes your coat, let him have your shirt as well. Give to everyone who asks you for something and when someone takes what is yours, do not ask for it back. Do for others just what you want them to do for you. "If you love only the people who love you, why should you receive a blessing? Even sinners love those who love them! And if you do good only to those who do good to you, why should you receive a blessing? Even sinners do that! (Lk 6:27-33)
To fully understand the difference in mentality between the pacifist, non-violent attitude of the Cordoba Martyrs and their violent, oppressive Moslem overlords, we should juxtapose the Moslem legalist al-Razi's defense of the jizya, the exorbitant and oppressive tax levied against Christians and Jews, to the wise words of the Redeemer quoted above:
The intention of taking the jizya is not to approve the disbelief of non-Moslems in Islam, but rather to spare their lives and to give them some time; in hope that during it; they might stop to reflect on the virtues of Islam and its compelling arguments and consequently converting from disbelief to belief. That's why it's important to pay the jizya with humiliation and servility, because naturally, any sensible person cannot stand humiliation and servility. So if the disbeliever is given some time watching the pride of Islam and hearing evidences of its authenticity, then apparently this might carry him to convert to Islam and that's the main rationale behind the enactment of the jizya. (Tafsir al-Kabir. Koran 9:29)
"…because naturally, any sensible person cannot stand humiliation and servility." Thus, by this Moslem scholar's own admission, Islam is not open to the possibility of humility and humble service to others—these aren't virtues extolled by Islam since no "sensible person" would practice them—the very two virtues Christ demands of His followers.
Islam and Christianity have nothing in common other than their monotheism but, considering their values, clearly the two religions do not worship the same Deity. Islam is certainly the cause of many wars. Christianity isn't.