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Keep in mind that the Islamic onslaught against Christians began in the 7th century and succeeded in conquering 2/3 of Christendom --- northern Africa, the Middle East, and SW Asia--- before the Western Christians began to fight back to regain the Holy Land (late 11th century.).
In intent, the Crusades were no more a campaign of aggression than the Allies landing at Normandy. They were trying to regain and hold what had been taken by Islamic fire and sword.
Here's a fascinating book, endorsed by anti-jihad activist Robert Spencer, about St. Francis of Assisi's attempt to convert the Sultan to Christianity during the Fourth Crusade --- The Real St. Francis, not the mythical soft-handed eco-hippie.
Aside from St. Francis of Assisi, the Crusaders didn't even try to convert the Muslims to Christianity. Maybe they should have?