So if God wanted to, He could have shed innocent blood by consuming Hiroshima with earthquake, tsunami, meteor strike. He is sovereign.
But it is clear and explicit from Scripture, verbatim, what God Himself finds abominable.
Deuteronomy 19:10
Do this so that innocent blood will not be shed in your land, which the LORD your God is giving you as your inheritance, and so that you will not be guilty of bloodshed.
Deuteronomy 19:13
You must purge from Israel the guilt of shedding innocent blood, so that it may go well with you.
Proverbs 6:16-17
These things the Lord hates: ...haughty eyes, a lying tongue, hands that shed innocent blood.
Jeremiah 19:4
For they have forsaken me and made this a place of foreign gods; they have burned incense in it to gods that neither they nor their ancestors nor the kings of Judah ever knew, and they have filled this place with the blood of the innocent.
Jeremiah 22:3
This is what the LORD says: Do what is just and right. Rescue from the hands of their oppressors those who have been robbed. Do no wrong or violence to the foreigner, the fatherless or the widow, and do not shed innocent blood in this place.
Joel 3:19
But Egypt will be desolate, Edom a desert waste, because of violence done to the people of Judah, in whose land they shed innocent blood.
Joel 3:21
Shall I leave the shedding of innocent blood unpunished? No, I will not."
And many other words of the Lord terrible and unmistakable.
Understand that I do not consider myself to be morally superior to Paul Tibbets or to anyone else. People do terrible things goaded by terrible circumstances. I just think the voice of God must be heard, though we hate like hell to hear it.
I bow my head as one who has no reason to boast.
Did you ever consider that God used America as His agent of divine retribution on an empire that shed an ocean of innocent blood from 1937-1945?
God knocked down the walls of Jericho, but afterwards the Israelites went in and put the city to the sword, apparently with God's blessing:
Joshua 6:20
20 So the people shouted when the priests blew with the trumpets: and it came to pass, when the people heard the sound of the trumpet, and the people shouted with a great shout, that the wall fell down flat, so that the people went up into the city, every man straight before him, and they took the city.
21 And they utterly destroyed all that was in the city, both man and woman, young and old, and ox, and sheep, and ass, with the edge of the sword.
None was spared except for Rahab and her family.
And in Deuteronomy 20:16:
16 But of the cities of these people, which the LORD thy God doth give thee for an inheritance, thou shalt save alive nothing that breatheth:
17 But thou shalt utterly destroy them; namely, the Hittites, and the Amorites, the Canaanites, and the Perizzites, the Hivites, and the Jebusites; as the LORD thy God hath commanded thee:
Judging from the history in the Bible, there are times when God condones the destruction of cities and sometimes commands it. I'm not implying that the United States was acting on specifically on God's orders, but instead was doing everything that it could to end the war quickly and victoriously. Oceans of blood have been spilled in humanity's wars throughout history. The enduring lesson of war is that only decisive victory brings lasting peace. The United States is arguably the most humane nation that has ever existed on the planet by virtue of its enormous power of destruction and its sparing use of that power. That is perhaps what irks its detractors, that something so powerful must be at its heart, evil, and yet it is not.