Now what was the grand result of all these struggles? [the Crusades] Europe expended millions of her treasures, and the blood of two millions of her children; and a handful of quarrelsome knights retained possession of Palestine for about one hundred years! Even had Christendom retained it to this day, the advantage, if confined to that, would have been too dearly purchased. But notwithstanding the fanaticism that originated, and the folly that conducted them, the Crusades were not productive of unmitigated evil. The feudal chiefs became better members of society, by coming in contact, in Asia, with a civilization superior to their own; the people secured some small instalments of their rights; kings, no longer at war with their nobility, had time to pass some good laws; the human mind learned some little wisdom from hard experience, and, casting off the slough of superstition in which the Roman clergy had so long enveloped it, became prepared to receive the seeds of the approaching Reformation. Thus did the all-wise Disposer of events bring good out of evil, and advance the civilization and ultimate happiness of the nations of the West, by means of the very fanaticism that had led them against the East. But the whole subject is one of absorbing interest; and if carried fully out in all its bearings, would consume more space than the plan of this work will allow. The philosophic student will draw his own conclusions; and he can have no better field for the exercise of his powers than this European madness; its advantages and disadvantages; its causes and results.
from chapter 9, paragraph 160, The Madness of Crowds