[CaptainHaplo]

It won't happen - for one reason. Who is going to fight it?

From the scenario you gave, the federal gov't. is going to use military force against the states. It would find the military would not be amendable to firing on civilians en masse to pacify the states. Nor does the political will by the people in any region exist that would allow for such a thing.

In the US Civil war, there were significant economic reasons behind the north wanting to invade the south. By conquering the south, the Northern rich could purchase through the spoils of war property in the south that, upon rebuilding - would bring them significant profit.

There is no such economic factor in place. Thus, there is no political will. Without this, the government would face revolt without geographic boundaries, and a revolt by the people at that level would bring the gov't to its knees, because its funding comes from the people.