To the first part of your post:

I don’t see the relevance. If the wife in our analogy stole the husband’s car on her way out the door, it wouldn’t justify his using violence to keep her in the marriage union itself. At most it would justify violence to get the car back. And even at that, we would question whether there wasn’t a better way to get the car back.

But to push it even further, the federal government is, as we say, “us.” It’s not some separate, independent entity. So I don’t know what property you’re referring to, but I assume if it was created or acquired while the union was still together, the South would have just as much claim on it as the North. Say, for example, the federal government builds a fort and stocks it with arms and supplies during the union, then after the split the South says, “This is as much ours as yours and since it’s on our land we’re occupying it,” the most the North could say would be that the South owes them half the value or whatever. But that’s just my two cents, not knowing exactly what you’re referring to.

To the second part of your post, that’s totally fair and I agree. I think that’s basically the way in which the War should be discussed, and I agree there is a tendency among Southern apologists to downplay, sometimes to an almost insulting degree, the role of slavery.