Honestly it might be because I'm approaching this from the perspective of a non-American outsider (although I've been studying American history since I was young because it's frankly vastly more interesting than Canadian history, hah) but I look at even Sherman's March to the Sea and I'm left thinking, 'seems pretty soft tbh'. I mean, in this same timeframe the Prussians were killing French civilians & destroying villages left & right in reprisal against
franc-tireur (French guerrilla) activity, the French themselves killed like a third of the Algerian population while colonizing that place, the Russians were deporting thousands upon thousands of Poles to Siberia after suppressing yet another Polish rebellion, the British were being the world's biggest and meanest drug cartel over in China, and where I was from the Dutch wouldn't even let our indigenous elites kill themselves -
even in 1906, decades after the ACW, they insisted on massacring the local princes and their families (who were already in the process of committing suicide!) with their own hands.
The number of countries, formal empires or otherwise, that let even their colonies - much less bits of them which they consider to be integral territories - to just walk away without a fight throughout history can be counted on one hand. Perhaps that is only natural for states in general, while the application of the ideal of self-determination is vanishingly rare in practice. But whatever the case, Lincoln at his worst really did seem to me like an absolute wimp compared to what the contemporary European powers were doing both in their colonies and to each other. I assume it's much worse from an American perspective because you guys actually had constitutional freedoms to lose in the first place and such, but were I a Chinese guy in the 1800s I'd definitely rather have dealt with Lincoln than Lord Palmerston, and were I Indonesian instead in the same timeframe I'd sooner put up with the Union Army of Sherman and Sheridan than the KNIL as well.
This is an argument of perspective and degrees I suppose. From an outside looking in, Lincoln is no great monster when compared to the monsters of the world, certainly.
But from the American perspective, he can be argued to be the first great monster that set the stage for even more abuses of the executive branch that we still suffer from to this day and heaped abuses upon people he supposedly considered his countrymen. Yankee and Southerner alike.
Sherman too, on the global stage, is nothing special. But under the microscope of the American system, he becomes something grotesque.
A man that unleashed his troops upon a civilian population with minimal if any actual efforts to rein them in. Cities were burnt, villages wiped off the map, many, many women raped and brutalized, slaves ironically freed from plantations only to be forced into labor for the union army or abandoned on the march.
His wife admitted, in a note to him, to her arousal at the thought that such a campaign would be carried out against the whole of the south and that they might be wiped out totally.
Sherman was a terrorist and a war criminal cut from the same cloth as all such men, and Lincoln unleashed him upon the southern states that he was supposedly fighting to bring back into the union.
“We have for years been drifting towards an unadulterated democracy or demagogism. Therefore our government should become a machine, self-regulating, independent of the man.” - William Sherman
Ultimately the northern elites were authoritarian in nature, desiring to finally squash the question of secession and, indeed, the very idea of states rights possibly superseding the rights of the federal government. The consequences of that can be seen to this day in America, even down to something as basic as how we speak about the country we inhabit.
As Razorfist put it, when an American is asked by a foreigner where they are from they will inevitably and inexorably say
the United States. Not Texas or California or any of the myriad other states or even territories within the union.
Pre-civil war the answer was the opposite. You identified with your state government first and the federal government second if at all. We were a union of independent states bonded together through shared culture, brotherhood, and the constitution handed to us by our founders.
Most importantly, it was a voluntary union, not something forced upon us at bayonet point. Indeed, if I’m remembering correctly, several states only joined with the tacit understanding that they could leave if they so desired.
Because of Lincoln’s administration, and the following Wilson and FDR (may they also rot in the deepest bowels of perdition), the stage was set for ever increasing totalitarian federal control of the country.
War time presidential powers were not even understood to be a thing pre Lincoln, and his assumption of them in the face of the constitution and congressional power is only one of the myriad of things that have effected the office of the presidency in negative ways.