Reconstruction was the method used to attempt to ensure a Republican form of government.
Can’t say I entirely agree with the method, but that was the theory. There are several ways Reconstruction would not have been so traumatic.
One would have been for southerners to accept that they’d fought a good fight but lost and would now have to adapt to that fact. Blacks would just have to be accepted as fellow citizens. Congressinal Reconstruction was to a considerable extent a reaction to southerners who started, fought and lost a civl war, then expected they could go on pretty much as they had before the war. Doesn’t work that way.
The other would have been for Lincoln to have survived. We can never know, of course, but it seems likely he’d have led a Reconstruction that wouldn’t have left so much bitterness behind.
BTW, in just about every other civil war in history, the winners killed tens or hundreds of thousands of the losers in revenge. The USA executed one man.
States became states during Reconstruction and it spread throughout the entire country. Federalism in the modern, Leviathan sense began then and remains today.