I appreciate what you say here, but secession is a political act, not an act of war. Don’t fall into that left wing trap. A seceding state(s) doesn’t ask for civil war, that would be insane. The seceding state(s) asks for their walking papers from the USA, if the Feds start something then....
Then the Feds are screwed several different ways, not the least being they wouldn’t get the tax revenue from that state anymore.