The American public imho has no stomach for a ‘Civil War’. If California (or any other state, for that matter) wants to leave…and, by that, I mean that an overwhelming majority of the people of that state have voted to leave…I think that serious discussions would have to be conducted about how to preserve the Union. Perhaps a constitutional convention that reduces the small state advantage in Senators and Electors could convince Californians that their issues, the reasons they want to leave, are being addressed.
Californians have many reasons to be alienated from Red State America. California is probably the leading state, at the head of the listing, of states that send more money to Washington than they get back. The political alienation and tension between liberal Californians and illiberal, wannabe theocratic Red States grows sharper every day. If the California exit people can focus those points, and many others, properly, they can get the overwhelming majority they need to be able to come to the negotiating table with a full mandate. Then, so long as ‘negotiations’ are going on, no one will put military force on the table.
The Red State problem will actually boil down to recognizing that their emphasis on ‘state’s rights’ will be in opposition to their possible desire to keep California, and then other states, from leaving. In this era, physical contiguity is not needed to create an alliance, even a nation.
In other words, if California really wants to go, if they threaten to suspend tax dollars to Washington, I just don’t believe that most Americans will support military action to take over the California government, when actual, decent and reasonable alternatives are obvious.
Two hundred and thirty years ago, banding together was essential for some degree of safety in a dangerous world dominated by wars between England, France and Spain. Great concessions were made to rural states in order to get ratification of the Articles and the Constitution. Today, perhaps, some concessions need to be made to the more urban states and more successful states economically in order to preserve the Union again.