A legal secession may be the best way to end an association but the Confederate democrats did not care about legality but were instead tyrants who usurped such power and were ruling tyrannically over citizens of the United States.
Any time one people disassociate themselves from another on this scale it is “legal” according to natural law. Men may try to mitigate their losses or stop them all together through use of man made laws and or arms but the only “court room” for this type of break up is the battlefield and the only “legal system” that matters is martial in its implementation. That is, if one side is determined to hold onto their slaves and the slaves are determined to be free.
As far as the conditions that existed before and during the civil war... Im not really that interested... Those men did their thing for their reasons good or bad, but now the only reason people bring it up is to try to spoil folks on the concept of actual secession. What we do, we do for our own reasons and the outcome will be different because of those reasons and justifications. We learn by history and apply its lessons to our present condition and future, but we NEVER let it shackle us to inaction and slavery.