Religious faith has always been a highly significant and powerful factor in human life throughout history; the prevalence of atheism and materialism in the west is recent development and an anomaly.

Anythng that is a powerful motivating issue has been used as a cause for war. Power, money. honor, ambition, family quarrels and prestige are other powerful factors and they usually can't be separated. Those who wage war will use anything that is important to people.

There is nothing surprising about that.

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My good blade carves the casques of men,
My tough lance thrusteth sure,
My strength is as the strength of ten,
Because my heart is pure.

"Sir Galahad," by Alfred, Lord Tennyson (1834)