The reason it was NOT a *civil war* or revolution, but a War for Independence, just as the American colonies of 1776 did not intend to overthrow King George and the existing government of Great Britain at the time, and as per the Rhodesian Unilateral Declaration of Independence of 11 November 1965.
Let's concentrate on pre-rebellion declarations, shall we? The colonist actions in 1776 was a revolution, a rebellion. They waged a war against the established government. Their actions were illegal under British law, and only the fact that they won and other countries recognized their sovereignty allowed the colonists to form a nation. Now, if the southern states had actually won their rebellion in 1861...