Most people did not care about blacks or slavery, but many did care (the blacks themselves as well as abolitionists in the North as well as lots of everyday people in the end). I am not in favor necessarily of taking down statues, but as far as the Confederate Battle flag goes, that should be nowhere except on your own private property. As one of the NASCAR sports commentators put it, it is not only the fact that the flag makes a lot of people uncomfortable, but also the fact that that was a flag of rebellion against the United States of America (let alone its close association with the institution of slavery)
The South didn't secede. They were fighting to keep things exactly as they had been, with each state making its own decisions. The North was fighting to institute new rules with a federal government dictating to the state governments. It was a conservative revolution. The South wanted to stay where it was. The North said we're going this new way and you have to come along. If we're playing soccer and i pick up the ball and run around with it and tell you "This is soccer now" you wouldn't be wrong to say it isn't since that's not what we had all previously agreed on.
Moreover, the North precipitated the war by sending federal troops to occupy Fort Sumpter, which is a real clear way of telling a state government that they will do what the federal government decides they will do, and that this control will be enforced at gunpoint if necessary. "United States" isn't a very good description. It implies that the states are freely united, by their own choice. "Subjugated States" would be more accurate.
Fwiw, I think the North was right practically and morally. There has to be a single, overarching governance of the land or there will be constant dischord. Doing away with slavery is morally imperative, even if that isn't why they did it. Legally tho, I think the South was right. The North was changing the rules and the South was within its rights to tell 'em to screw off.
Emancipation was a military strategy. Lincoln didn't say all the slaves are henceforth free. He declared that slaves were free anywhere a Union army took control. It was designed to encourage guerrilla involvement from the large slave population and turn that enemy asset into a liability.
