[r9etb]

since the duly-elected governments of those states were the civil authority.

Those duly-elected governments had authority only insofar as they do not contradict the Constitution.

[The Green Goblin]

Those duly-elected governments had authority only insofar as they do not contradict the Constitution.

Exactly. Since the Constituion does not explicity prohibit the secession of the states, that right is reserved (under Article X) to the states, or to the people.