"Every act of war directed to the indiscriminate destruction of whole cities or vast areas with their inhabitants is a crime against God and man, which merits firm and unequivocal condemnation." -
Para 81, Constitution on the Church in the Modern World.
And part of Just War doctrine.
When they wrote that, the Church fathers failed to interview the priest who was my hs teacher, a US chaplain on the Bataan Death March.
Most of the debate on use of atomic bombs on Japan misses this point. The focus of the debate is always on the bomb, not on the target. In my book A Fighting Chance: The Moral Use of Nuclear Weapons, I apply Just War Doctrine to the use of nuclear weapons. My conclusion: the attacks on Hiroshima and Nagasaki were immoral, not because atomic bombs were used, but because they were targeted at cities full of noncombatants.
I once read a memoir by a Japanese submarine officer who had been stationed at a sub base near Hiroshima when the bomb was dropped on that city. He described the bombing from the standpoint of a nearby observer. Rather than attacking the city, the sub base should have been attacked. Yes, there still would have been some damage to the city, but the attack would have satisfied the Just War criterion of Discrimination, that is, attacks should be on the enemy's military forces, not on noncombatants. Whether it would have satisfied the other Just War criterion of Proportion is impossible to determine now, but my guess is, it would have. That is, the damage done to noncombatants (collateral damage, in the current vernacular) must not exceed the good done by the attack on a legitimate target.
Those who point to lives saved by the bombings are, whether they realize it or not, appealing to the Proportion criterion. Yes, the atomic bombs cost many lives, but they saved many more. However, Proportion is trumped by Discrimination. First of all, the attack must be against a legitimate target. Only after Discrimination is satisfied can one even ask about Proportion.
FWIW, I teach Just War Doctrine at Yorktown University.
Also FWIW, my father was stationed at an amphibious training base in California in 1945, and would have been manning a landing craft during the invasion. Yes, I'm glad the war was brought to an end without an invasion. However, I wish the bombs had been used in accordance with Just War Doctrine.
By this doctrine then, Japan prevails in the war. See Manila for a city fight against the Japanese.