This is America which is not Vietnam, Serbia, Uganda, or even Iraq.
You dreaming you have a clue how things would be here would be a mistake, as I have already mentioned.
They could tell the commander of the Second Armored Division to suit up, tank up and roll on Houston, and the commander could talk to his troops, load up the tanks and say, "I don't think so Tim, and we're rolling on you motherfuckers."
You are assuming that federal lines will hold in a civil war, which means you don't know what a civil war is.
It doesn't necessarily mean a military operation on civilian combatants, and the military combatants may freely choose what side they are going to fight on in a civil war, and they might just bring everything on base with them.