Ridiculous fantasy. Name a single time in history that has EVER happened.
Look at Eastern Europe !
1. Czechoslovakia breaks into the Czech Republic & Slovak Republic.
2. USSR breaks up in 1991, only recently has conflict started and this conflict pales to insignificance compared the Russian Civil War 1917-1923.
So it can occur under the right conditions !
In the US a “break-up” will be difficult and I can see the possibility of violence. The differences now don’t easily break down across geographical lines like the last time.