War is a sin, on a global level, to describe the majority opinion.
Such a pity then that in the last World War, and no doubt in all wars, both sides believed that God was 'on their side' - as if God would take 'sides' in such things! If this mythical being really did exist she would be pulling her hair out in despair at the way humans have been behaving.
Fortunately, there is no such thing as 'God' the phenomenon is just thoughts in the minds of those who believe - after all, there are so many different deities. If there was only 'One God' then everyone worldwide would agree what this being is and all would believe in the same being. In fact, different cultures believe in different Gods, some believe there are many Gods and some believe there is only one of them.
No point in quoting the bible to prove anything, as so many believers do. They quote from the bible as if mere quotation were enough to prove the point. It isn't. Best to stick with reality, quoting myths doesn't help the discussion.