The census of 1939 in Germany listed the following; 54% Protestant, 40% Catholic, 3.5% believer in God, 1.5% non-religious, 1% Jewish. In total over 95% of people living in Germany were Christian. In 1933 there were approximately 45 million Protestants in Germany which at that time was 67% of the population. In 1937-38 Germany annexed Austria which was a large majority Catholic. 
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In 1939 with the annexation of Poland Catholics were persecuted along side German Catholics in Dachau, 2720 died there including 1,034 priests.
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Catholic schools were shut down in 1939 and the Catholic press in 1941. The German government took over many churches, monasteries, convents and church properties for the public interest. The Nazis attempted to eradicate the Catholic Church in areas outside Germany, mainly Poland to a smaller extent Slovenia and Austria.
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Whoever wrote "Christians don't do this kind of thing" doesn't know their history!
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Christians were fighting Christians!