[ZULU]

That's not really accurate here.

The legally, duly constituted governments of several states, elected by the citizens and reflecting the sentiments of the majority of them, voted to remove themselves from a civil compact they had willingly entered several decades before.

A "Civil War" is more properly a situation as existed in Englan in the 1660's when fighting broke out between Royalist forces and Puritan Parlimentarian forces all over England. In this situation, there was no attempt to establish an independent state, but rather to overthrow an existing government.

[Non-Sequitur]

The legally, duly constituted governments of several states, elected by the citizens and reflecting the sentiments of the majority of them, voted to remove themselves from a civil compact they had willingly entered several decades before.

Since they lacked the authority to do so then their actions were illegal and constituted a rebellion or a civil war, take you pick.