The Just war theory says that when there is a legitimate military target, civilian deaths must be proportionate to the value of the target and must be totally incidental. So, you can’t use the presence of a single factory as a pretext to destroy an entire city. The means to achieve the military objective must use the minimum force necessary.
But Dauphin, you can’t use minimum force when the enemy refuses to surrender. Once the war starts (remember Japan started it, not the U.S.) the U.S. had to prosecute the war to its conclusion.
The Japanese had shown no inclination to surrender, zero. They were preparing their entire population (women and children included) to resist an invasion to the last person. They were arming women and children with spears to fight American troops.
Given the weapons of the period, it was not possible to target individual buildings, like factories, which were in built up areas. Any attack, conventional or nuclear, would kill many civilians.
I abhor the targeting of civilians, and I think you have a good case that the firebombings of Germany were war crimes (because the Germans showed willingness to give up when militarily beaten). It is quite likely that the war would have ended much earlier, without the Soviets gaining all of Eastern Europe if it wasn’t for Roosevelt’s ridiculous unconditional surrender demand.
But, the Japanese just refused to surrender. Given that, the only moral option was to end the war with as little loss of life as possible. It was a choice between 4 bad options 1) invasion 2) conventional bombing 3) starvation blockade and 4) atomic bombing.
The death toll among Japanese only would have been orders of magnitude higher under the first 3 options. Millions dead, not 100-150,000. Not to mention all the Allied troops, POWs, and innocent civilians under Japanese rule in Asia, that would have perished in another year or more of Japanese rule.
There really isn’t any “minimum force in war”. Does that mean I must attack my enemy with a knife, if the bullets might hit a civilian.
Aquinas has 3 criteria for just war.
First, the authority of the sovereign by whose command the war is to be waged…
Secondly, a just cause is required, namely that those who are attacked, should be attacked because they deserve it on account of some fault…
Thirdly, it is necessary that the belligerents should have a rightful intention, so that they intend the advancement of good, or the avoidance of evil.
God Bless