I have no doubt that He would intervene on a nation's behalf. I'm only stating that we're still subject to His law at all times. (It's not up to us to carry out the murder of innocents simply because we decide we're in the right.)
The Germans also believed that they had Divine Providence on their side; does a moral right or wrong come down to nothing more than simply being on the winning or losing side?
But it wasn’t murder. Therein lies the issue. Collateral damage on military targets is war, and that is always been the scope of war. Limiting death to military personnel has always been unavoidable. Don’t start a war if you have a distaste of harm coming to your citizens. War has never been clinical.
Any nation invoking Divine Providence had better align itself with the Divine, less they be rebuked. Both Germany and Japan were rebuked. If you dig into the Nazis you will discover its leaders were deep into the occult. Japan’s mistaken beliefs are manifest.
Which Law’s of God are you invoking? The Deca Law? God gave the sword to government for a reason: to punish the wicked. Both Germany and Japan were wicked. Rulers are not a terror for good, but for evil, and they carry a sword to carry out God’s wrath (Romans 13:3-4).