When the harm wrought by war is not comparable to that caused by tolerating injustice, we may be obliged to suffer injustice, declared Pope Pius XII in his Address to the World Medical Association on October 19, 1953. In other words, Pius XII held that the human and natural damage wrought by a nuclear strike was out of proportion with any aggression whatsoever. Indeed, in response to the aforementioned nuclear bombings of Japanese civilians, Pius XII declared that every act of war directed to the indiscriminate destruction of whole cities or vast inhabited areas is a crime against God and man.
And, dare I mention, God. He states about a dozen times in the OT that the shedding of innocent blood is an abomination. Abomination like sodomy. Abomination like child sacrifice. Like "the Abomination of Desolation."
See #15.