For the South, it was rather simple: they were invaded
For the North, it was rather simple: the states seceded
But we all know it goes far deeper than that on either side.
The legal quibbling over the inherent right of a state to leave the federation is best left elsewhere. I have read statements from better legal minds than my own on this question and have to say it is still up in the air. My opinion is in agreement with Abraham Lincoln, when he argued in Congress that secession was a grand and glorious thing… of course he was speaking for Texas seceding from Mexico, but his argument was valid for any secession.
I do know that someone complained that the South could not leave because they had signed the Constitution and it was a contract.
Well, I have studied a little law and I know the Constitution is NOT a contract. A compact, yes, but a contract, no. Any contract drawn up to be perpetual is tacitly illegal. All contracts have an “escape clause” for either of the contracting parties. If the Constitution had been a mere contract, there would have been a secession clause explicitly written in it or it would have been nullifiable.
On whether the Confederacy was actually a separate nation – since no other nation recognized them as such – is left elsewhere as well (though I will touch on it in a later installment as it deals with more than this one issue). With the Northern blockade in place, it was unlikely that the South could ever make contact and gain such recognition. It is said that Britain and France were waiting for the Confederacy to string together a string of martial victories before they would recognize them and offer support.
To the North it was a civil war – an internal rebellion within a single country – since they did not recognize the right of the states to secede. The South recognized such a right… but then so did Lincoln, as I mentioned above when he argued for the righteousness of secession when the northern parts of Mexico wished to secede from their nation. He likewise was fine with the secession of West Virginia from Virginia.
I think, personally, that his stand on secession was – like most people – used when it served his needs rather than as a firm legal concept.
But, like I said, I will leave that to be argued elsewhere.