That is exactly what they did. An individual state could no more unilaterally remove itself from the Union without the permission of the others than the other states could expel a member state without its consent. It is the nature of the contract.
It could have been legal if they had either passed an amendment giving states a unilateral right to secede or even if the congress as a whole voted to allow a state or states to depart the same way as congress votes as a whole to admit new states. The South attempted neither and they may well have been successful if they had tried. Instead they chose open rebellion.
and those of Mr. Jefferson shortly thereafter
Jefferson had no role in writing the Constitution. And his ‘words’ tended to change considerably depending on what ax he was grinding at any give moment. He was not a model of consistency. If I read him right, he surely would not have tolerated secession during his eight years in office. When he waxed on at Montecello about the evils of slavery or whatever he may have divined such a right, but the actual framers did not. Neither Madison or Jay saw a right to secede. The writings of Hamilton and Washington strongly imply that they saw no right to do so either. These are people who sat in Philadelphia in the summer of 87 and wrote that document. They clearly viewed the Constitution as a perpetual Union. It would be foolish to think these men who understood how very difficult representative government was would spend their time devising a Union of 13 states thinking that at the first storm, or the first disappointment, those states could simply pack up and depart. These were very practical men. They would not have wasted their time writing a fragile document such as that.
If the south were being oppressed in 1860, the Founders would have supported armed rebellion. But exactly how was the south being oppressed by the Federal Government? There only grievance seemed to be that many in the North didn’t like slavery and were helping slaves escape and teaching them to read. The Federal government wasn’t helping the slaves escape or teaching them to read. Private citizens were. So the south rebelled and started a war. Where’s the justification?
Allow me to correct you: “the nature” of a contract is to include binding terms in writing. The constitutional contract nowhere prohibits secession – period. Now you may believe in the validity of ‘unwritten laws’: that is certainly your right. I can only wonder what you would say if your finance company advised you that you owed another 36 (or 72, or 144) car payments above and beyond what your contract specified, in writing, simply because that was their understanding of “the nature of the contract.”
It could have been legal if they had either passed an amendment giving states a unilateral right to secede or even if the congress as a whole voted to allow a state or states to depart the same way as congress votes as a whole to admit new states. The South attempted neither and they may well have been successful if they had tried. Instead they chose open rebellion.
No amendment was required: as Senator Toombs noted at the time, the Tenth Amendment declared, in writing, that all powers not delegated nor prohibited (including, by definition, secession) by the Constitution were reserved to the people of the States. The written words of the Constitution trump any supposed ‘unwritten law’...
Jefferson had no role in writing the Constitution...
Your arguments are perfectly compatible with an ‘unwritten law’ foundation. You seem to suggest that those who had “no role in writing the Constitution” could not possibly understand its terms. You would most certainly be correct, if the compact was composed of secret handshakes, confidential agreements, and ‘unwritten laws.’ That, fortunately, is not the case. The Constitution is a written document, and it is quite specific: powers not delegated nor prohibited are reserved, not to the federal government (as the proponents of ‘unwritten law’ seem to suggest), but to the States and their people. As Mr. Madison observed:
“The powers delegated by the proposed Constitution to the federal government are few and defined. Those which are to remain in the State governments are numerous and indefinite.”
Nowhere does the Constitution ‘define’ a federal power to prevent secession; rather, the States retain that power (among those which are “numerous and indefinite”). This is perfectly in keeping with the written terms of the Tenth Amendment.
But exactly how was the south being oppressed by the Federal Government?
I have addressed this point previously (Post #372).
Allow me to ask you a somewhat related question: if the citizens of another State violated their written obligations under the Constitution, and the federal government refused to enforce those written obligations, would you take exception to their conduct? Would you consider either entity to be in compliance with the written terms of the compact?