95% of all Germans were Christian in 1939, 45 million Protestant and 20 million Catholic. 13.1 million soldiers fought in the war 4.8 million died. For you to say all 13.1 million soldiers abandoned their religion is absurd. 
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To further prove Christians killed Christians, between 650,000 and 850,000 civilians were killed during the bombings in Germany. The vast majority Christians. 
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Read, Small Christmas Truce, of  WW2. https://owlcation.com/humanities/About-World-War-2-A-Small-Christmas-Truce
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Wars where Christians killed Christians; Revolutionary War 24,000 British,  8000 Americans,  Spanish American  4234 Filipinos, Mexican American War 13000 Americans, 25000 Mexicans, Civil War 620,000 died.
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You state "Christians don't do this kind of thing" the facts speak for themselves. You are obviously in denial and don't know your history!
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How do you like that!