The first came from a snip from Federalist 39, which my friend posted on Facebook.
"Each State, in ratifying the Constitution, is considered as a sovereign body, independent of all others, and only to be bound by its own voluntary act."
It seems to me that if they are "only to be bound by [their] own voluntary act", if they change their minds at some future date, they should be free to go. But this is a single sentence, so I went looking for more context. Turns out that one of the charges brought by the Anti-Federalists was that the Constitution was going to create, rather than a confederacy, a consolidation of the States. Confederacy has become, since the Civil War, something of a bad word, but that wasn't always the case. In Federalist 9 Alexander Hamilton comes right out and says that the Constitution will create a "Confederate Republic" (emphasis original).
To this catalogue of circumstances that tend to the amelioration of popular systems of civil government, I shall venture, however novel it may appear to some, to add one more, on a principle which has been made the foundation of an objection to the new Constitution; I mean the ENLARGEMENT of the ORBIT within which such systems are to revolve, either in respect to the dimensions of a single State or to the consolidation of several smaller States into one great Confederacy. The latter is that which immediately concerns the object under consideration.
At this point, I'm uncertain as to what, precisely, they mean by "Confederacy", since the word has fallen out of favor. Happily, Webster's 1828 Dictionary is readily available online, and those definitions are much closer in time, and thus very likely in meaning, to what Hamilton and Madison and the rest would have understood the word to mean.
Hamilton asserts in Federalist 9 that the difference between a confederacy and a consolidation is "more subtle than accurate", but I'm not convinced that the evidence that he himself brings to the table supports that assertion. To me, that seems to be a ploy to diminish the concerns of the readers on the matter; they are, after all, battling for public opinion in these essays. He quotes an extended passage of the writings of Montesquieu, including the following (emphasis mine):
1. A league, or covenant; a contract between two or more persons, bodies of men or states, combined in support of each other, in some act or enterprise; mutual engagement; federal compact.
The friendships of the world are oft confederacies in vice. A confederacy of princes to check innovation.
2. The persons, states or nations united by a league.
Virgil has a whole confederacy against him.
3. In law, a combination of two or more persons to commit an unlawful act.
"Should a popular insurrection happen in one of the confederate states the others are able to quell it. Should abuses creep into one part, they are reformed by those that remain sound. The state may be destroyed on one side, and not on the other; the confederacy may be dissolved, and the confederates preserve their sovereignty."
This, combined with the statement that first caught my attention, leads to a couple of conclusions:
1. The South should have been able to succeed peacefully. If it really is a voluntary association, then any party ought to be able to walk away at any time. For freedom of association to be meaningful at all, there has to be also the freedom not to associate.
2. The Civil War may have been about slavery. But it probably was also about States' rights. And from that point of view, it seems to me that the entire country lost. The difference between "these united States" and "the United States" is huge.
3. I still don't have enough information to know how much of that change from a Confederate Republic to a single nation, if any, Mr. Lincoln was responsible for. However, I am now of the opinion that the South should have been allowed to walk away. At least, that's what I think pending further information.