The nuclear attacks on Japan are actually the perfect example to demonstrate the rules of war.
First, the attacks were not punitive. It was not simple retaliation or lust for war. If they were, they would be a war crime.
Secondly, the attacks pass the proportional proportionality analysis. In the case of Hiroshima, the military objectives were the neutralizing of the 2nd General Army, the 59th Army, the 5th Division, the 224th Division, 5 anti-aircraft batteries under the 22nd separate and 45th separate anti-aircraft battalions and the 121st and 122nd anti-aircraft regiments, it was the location of a supply and logistics headquarters, it was a stepping off port for the movement of troops, and it had factories for the manufacture of aircraft, ships, bombs, rifles and handguns. Those are clearly defined military objectives. Hiroshima housed over 440,000 soldiers with only about 340,000 civilians, and the end goal was to end the war without engaging in a land invasion which would necessarily include bombing and naval bombardment and was estimated to cost millions of military and some number more then that civilian lives on the Japanese side alone.
For Nagasaki, it was a naval industrial hub housing almost all of Japan's naval manufacturing as well as a supply and logistics port. Despite these military objectives, the loss of life was still considered, primarily it was one of the least populated cities with military objectives and of all potential targets had the largest number of people involved in military manufacturing at over 90% of all persons present. At the time of the raid, it was estimated that less than 300,000 people were in the area, and that primary goal again factored in the millions of lives that would be lost in the event of a land invasion.
The result was a significant shortening of the war, the decimation of Japanese military manufacturing, particularly naval manufacturing, the neutralization of an entire General Army and several smaller units, and the savings of millions of lives that would be lost in a land invasion, at the expenditure of about 600,000 civilians. The Japanese Imperial Army had told the allies they would need to defeat 20 million Japanese soldiers, and civilian losses are always higher, so 600,000 civilians and 500,000 soldiers were compared to 40+ million Japanese and some dozen or more million allied soldiers. Under proportional proportionality analysis, the bombings were not war crimes.
The post I replied to had said Israel was attacking civilians deliberately in order to get to them to give up their support of Hamas. If so, that is indeed a war crime. That is not a defined military objective as it is pure reciprocity. It's also illogical and insane to think killing someone's family and destroying their home is going to get them to hate your enemy. They're just going to hate you. Israeli is creating more Hamas support, not reducing it. It's also never worked in history. It's a losing strategy. Either Israel has lost their mind, that's not the objective at all, or they are simply killing Gazans for the sake of killing Gazans. It was too be one of those three. It's possible there's some objective we don't know about, and possibly that would pass the proportional proportionality analysis, but no military expert that's studied this that I follow can find that. The conclusion in military circles is clear: Israel is engaged in war crimes.
I don't necessarily disagree with you. I do, however, still disagree that they are justified in committing purely punitive attacks against a civilian population in direct violation of the Geneva and Hague Conventions, and I think it's lunacy to believe that the result will somehow be less support for Hamas.