“If the entire state secedes then they are a separate country.”
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What happens when the central government....i.e., the federal government....won’t let them have their independence?
The last time a group of states tried that, in the early 1860’s, it did not turn out well for them.
I think we learned form the last time that starting a war over the secession of a state(s) is a really stupid idea. The USSR dissolves with very little bloodshed at all.