The South did not appeal to legality because they would have lost. They appealed to the sword, and lost.
The US existed before the current constitution according to the Articles of Confederation, in a perpetual union. Robert E. Lee admitted as much. Pity he didnt act on those convictions, rather than on his misplaced loyalty to his State.
I would have to agree that the South was not really a well-established, functioning Democracy in 1861.
It is debatable. We could say it about North: "The North did not appeal to legality because they would have lost. They appealed to the sword, and WON."