“What about the military?”
In the War Between the States many Southerners were allowed to leave the US Military and subsequently fought for the Confederacy.
“OK, each state now has its National Guard. Cant the president call them to national service and put down any rebellion by a state government?”
Sure, the president can call them. If you mean can he have the National Guard put down a rebellion by a state government when it is the home state of those Guardsmen, that’s problematical. Many or all of them might fight on the side of their home state. If you mean can he send in the National Guard from another state, that could be problematical too. If we’d had the National Guard at the beginning of the Civil War, before North Carolina seceded, would the North Carolina Guard have helped put down the rebellion by the State of South Carolina? I kind of doubt they would have followed those orders.
“Then too, what about the national military already stationed in the states. Couldnt the federal government use them to prevent states from splitting off (Civil War?).”
I don’t think there are enough of them in any one State if the people of the State get involved, and I doubt the State Government would take action if it didn’t have a substantial number of the people behind it.
During the War Between the States the national military in terms of the Regular Army wasn’t large enough to do the job either. Volunteers from the Northern states bore the brunt as opposed to the Regular Army.
OK so what about Fort Bragg? Or say Parris Island, military training bases have lots of troops ... So what if North Carolina wants to leave the Union? Same thing all over again?