[FLT-bird]

That was 1830 so in 1860 South Carolina was careful to enlist the entire Deep South in secession, and make the reason slavery, not tariffs.
But while protecting slavery sold well at home, it won no friends in Europe, and so was jettisoned there in favor of “free trade” and “oppressive Federal government.”

And that Confederate argument seemed to work pretty well, until Lincoln blew it away with his Emancipation Proclamation.

This is a PC Revisionist lie. The Lincoln administration and the Northern dominated Congress was only too happy to offer the Corwin Amendment which would have expressly enshrined protection of slavery effectively forever in the US Constitution.

The US Congress then passed a resolution stating that they were not fighting over slavery.

Meanwhile of the 7 original seceding Southern states only 4 issued declarations of causes. Of those 3 of them listed tariffs and unequal federal expenditures along with some added complaints about the failure to provide border security by Texas. THEN Lincoln chose to start a war. THEN 4 and arguably 5 more states seceded. Obviously they were not seceding over slavery but instead over the principle that government derives its legitimacy from the consent of the governed as had been stated in the Declaration of Independence.

[BroJoeK]

So let's start here:

FLT-bird: "THEN Lincoln chose to start a war.
THEN 4 and arguably 5 more states seceded.
Obviously they were not seceding over slavery but instead over the principle that government derives its legitimacy from the consent of the governed as had been stated in the Declaration of Independence."

Obviously not over slavery, but following Virginia's lead and Virginia could only declare secession after its Constitution signing statement conditions were met:

"...powers granted under the Constitution, being derived from the people of the United States may be resumed by them whensoever the same shall be perverted to their injury or oppression..."

Jefferson Davis well knew that Virginians believed they could not declare secession until that condition was met -- "injury and oppression" -- and in April, 1861, it had not been.
That's why Davis needed war at Fort Sumter -- it moved Virginia from Union to Confederate and along with Virginia, Tennessee, North Carolina and Arkansas.
It might even bring in Kentucky, Missouri & Maryland, but regardless, the payoff for Davis from starting war at Fort Sumter was beyond huge, it was transformative.
It almost doubled the Confederacy's size & population, adding vital manufacturing capacities, and making Civil War a serious contest.

So, "Injury and oppression" is what Davis provoked at Fort Sumter, and it won him the entire Upper South.

FLT-bird: "Meanwhile of the 7 original seceding Southern states only 4 issued declarations of causes.
Of those 3 of them listed tariffs and unequal federal expenditures along with some added complaints about the failure to provide border security by Texas. "

No, ,none of those four mentioned either tariffs or taxes.

1. South Carolina went first, December 24, 1860, and mentions at slavery length, nothing else.

2. Mississippi came next in January 9, 1861, mentions only slavery, nothing else:
   
   "Our position is thoroughly identified with the institution of slavery -- the greatest material interest of the world.
   Its labor supplies the product which constitutes by far the largest and most important portions of commerce of the earth..."

3. Third was Georgia, January 29, 1861, and it does complain briefly about matters other than slavery:
   "Even the owners of fishing smacks sought and obtained bounties for pursuing their own business...
   The manufacturing interests entered into the same struggle early, and has clamored steadily for Government bounties and special favors.
   This interest was confined mainly to the Eastern and Middle non-slave-holding States."

   First note here the word "mainly", it means that Southerners also received "bounties" to the degree they participated in those activities.
   And actual data clearly shows the South got its "fair share" & more of Federal spending.
   So, does anybody seriously suggest that after 70+ years, Georgia declared secession over "bounties" paid to fishing smacks or "protection" to manufacturers?

   Indeed, Georgia fully admits:

   "After having enjoyed protection to the extent of from 15 to 200 per cent. upon their entire business for above thirty years, the act of 1846 was passed.
   It avoided sudden change, but the principle was settled, and free trade, low duties, and economy in public expenditures was the verdict of the American people.
   The South and the Northwestern States sustained this policy.
   There was but small hope of its reversal; upon the direct issue, none at all."
   
   Georgia admits that Southern concerns were satisfied in 1846!
   All the rest of Georgia's long statement is devoted to slavery.

4. Finally Texas, February 2, 1861, does complain that Robert E. Lee did a terrible job of protecting them against Indians and "banditti", so doubtless they were glad to see Lee move back to Virginia.
   Texas also complains that Northerners:
   "...have impoverished the slave-holding States by unequal and partial legislation, thereby enriching themselves by draining our substance."

   Of course that's bogus, data shows the South got its fair share & more of Federal spending.
   All the rest of Texas' long statement is devoted to slavery:

   Abolitionists "demand the abolition of negro slavery throughout the confederacy, the recognition of political equality between the white and negro races, and avow their determination to press on their crusade against us, so long as a negro slave remains in these States."

So for most, slavery was the only reason and for all, slavery was the most important reason.
It was all about slavery.

FLT-bird: "This is a PC Revisionist lie.
The Lincoln administration and the Northern dominated Congress was only too happy to offer the Corwin Amendment which would have expressly enshrined protection of slavery effectively forever in the US Constitution."

No your Revisionist lie is to imply that slavery was not the single greatest reason, indeed the only reason for most, why the first seven states declared secession.
As for the proposed Corwin Amendment, Lincoln's opinion was that it only restated what the Constitution already, in effect, said.
Corwin changed nothing, in Lincoln's opinion, so he did not oppose it.

But by March of 1861 the secession states were uninterested in compromises to restore the Union.
What they wanted most was for the Upper South & Border states to join their Confederacy, and for that they needed Virginia, and Virginia would only secede in the event of war.

Hence Jefferson Davis' assault on Fort Sumter.