I see your thought process on this Alan. I also agree Sherman was nowhere near as ruthless as 20th century warriors.
There are however fundamental differences. Setting aside the technology for mass destruction. Striking at the heart of mainland Japan, and blanket bombing German cities. Was a major, psychological blow to the peoples of those nations.
Beginning with Doolittles stretched raid to bomb mainland Japan, at high cost to his own pilots. There was a desire to deliver "retribution", to the citizens who supported the war effort. Similarly, there was a lust for revenge against German people, who had been portrayed as Nazi sympathisers by our own propoganda machine.
The greatest difference with Japanese, was their appearance. You could say it was racist. But they were recognisable as "different". Germans not so much, but they had certainly been portrayed as evil, and sub-human by their attrocities and underhand tactics during the long war. Creating an itch for payback.
Some have mentioned the Spanish Civil war. This too was a ruthless, snuffing out of resistance against facism. By any method regardless of consequence. A real dirty affair, the fallout of which is still harboured today as deep resentment in some regions.
Other rebellions, as some have mentioned were also, subjegating native populations to the will of the Imperial master. Also a racist slant perhaps. But little mercy or respect was shown to the victims.
Then we come to the ACW.
These were people who had more in common, than perhaps they cared to admit. They had built a nation together, and were now in the process of deciding its final direction.
For 4 years they had struggled to the death on various battlefields. The combatants had gradually developed a respect for each other. Which may have been missing at the outset.
Many recognised images of their own wives and children within civilian populations. They would be cold-hearted killers to put women and children to the sword. Again, I will say, Sherman was not such a person. Not to say some within the ranks may have been, but they would be few, and regulated by orders of limitation.
And then I come to the race of people in the ACW, who were clearly different to the majority. The slaves, and USCT. If someone was to be blamed for bringing such loss and sorrow at the end of the war. Here was an easy opt out. There would be no hiding place for people of colour. Prejudices would last another hundred years. From both those who fought to free them, and those who fought to keep them enslaved.
I would venture an opinion, that ACW veterans would mostly shake hands with former enemies than, shake hands with a black man. Even though he may have fought on the same side.
Here was the cause of the war, and a race of people who now required a place in society. It was long denied, and once more the, now free, black population was set aside. While America rebuilt.
Finally back to Shermans tactics, towards the people of the South. His aim was to break the legs of the structure. Not drive a stake through its heart. He did this thoroughly, with a kid glove on one hand, an iron gauntlet on the other. These bretheren, sisterhood and children of the South. Would be the new Americans of tomorrow. It was the vision of Lincoln to let them up easy. Even Sherman would have had to answer to him otherwise. Yes it was ruthless, but also limitations. This war up to then, had been an honourable struggle for the most part.
Unlike the other wars to which you refer Alan. From the start there was little or no honour. No surprise there was none at the end.