[LTCJ]

Most of the states didn't voluntarily join anything. They were allowed to enter the Union, admitted only after a majority of the existing states gave their approval through a vote in both houses of Congress. Shouldn't leaving have the same requirements as entering?

Any people anywhere, being inclined and having the power, have the right to rise up, and shake off the existing government, and form a new one that suits them better. This is a most valuable,-- most sacred right--a right, which we hope and believe, is to liberate the world. Nor is this right confined to cases in which the whole people of an existing government, may choose to exercise it. Any portion of such people that can, may revolutionize, and make their own, of so much of the teritory as they inhabit.

[Bubba Ho-Tep]

Ah, so you know Lincoln's Mexican War speech. And there's no doubt that the south had the natural right of rebellion. Of course, southerners have expended a great deal of ink and hot air over the generations specifically denying that their actions were rebellion or revolution (which is just a word for a successful rebellion). The Creed of the Children of the Confederacy, the UDC junior auxilliary, for example, explicitly says so.

The catch with the natural right of rebellion is that there's no obligation for the other side to bend over and take it. As Lincoln says, "such people that can, may." The south couldn't, as it turned out.

[LTCJ]

Oops - inadvertantly left out the citation:

Any people anywhere, being inclined and having the power, have the right to rise up, and shake off the existing government, and form a new one that suits them better. This is a most valuable,-- most sacred right--a right, which we hope and believe, is to liberate the world. Nor is this right confined to cases in which the whole people of an existing government, may choose to exercise it. Any portion of such people that can, may revolutionize, and make their own, of so much of the territory as they inhabit.

- Abraham Lincoln