They didn't need to believe him. It was literally impossible with 16 slave states in the Union to get the votes necessary to override their opposition. Slavery could not be legally abolished in that era because they couldn't possibly get enough states to vote in favor of this.
Slavery was going to be left untouched wherever it existed anyway.
Besides thinking they could win a war against the north,...
I expect they never believed the North would go to such great lengths to stop them. I'm sure they thought it would work out in the same manner as the American War of Independence. Given that our own Declaration recognized Independence as a right, it was reasonable to believe that people would simply accept their right to gain independence.
they also thought that embargoing cotton sales to Britain to bring that anti-slavery nation into the war on their side being two glaring examples.
Yes, that seems to be rather bone headedly stupid, but I haven't examined that bit of history much. My focus on the civil war has always been on why it happened and who was responsible for starting it and why. After it started, It was a foregone conclusion who would win it. It never should have started.
If, after secession, California authorities used their National Guard to violently attack Edwards AFB, would any President not respond?
Not quite the same thing. More like, if California seceded, and the US Army decided to take over Alcatraz and threaten shipping, and then California tried to talk them into leaving for three months or so, and then a war fleet shows up to attack the Defenders of San Fransisco, *THAT* would be a closer analogy to what happened.
The Confederates had been told by the Secretary of War that all the forts surrounding the entrance to Charleston bay would be turned over to them. The "National Republican" newspaper had also announced that the Fort would be turned over to the confederates.
They no doubt felt that they were within their rights as a sovereign nation/state. Lincoln thought the attack justified a military response.
Lincoln sent the fleet of warships with the deliberate intent of provoking a military response. There was not a cargo ship among them. 5 ships of war, and two, possibly three armed tugboats. The "Baltic" was carrying at least 200 riflemen, shells, powder, and other equipment of war.
Could all of this been avoided. Of course, but sooner or later the issue of slavery, which was behind all of it was going to have to be addressed.
It would have waned in the South, same as it did in the North. It would have just taken longer.
Very few ‘first-world nations’ in 1860 still had slavery.
That's because they weren't producing 230 million dollars per year from it. If you can't make it pay, people can suddenly see moral reasons to get rid of it. None of the other first world countries had any problems buying their goods though.
It would have waned in the South, same as it did in the North. It would have just taken longer.
By the 1860s the handwriting was on the wall. Where were future cotton-growing areas to come from? There was even talk of annexing Cuba to continue cotton/slavery. Too much of the south’s capital was invested in its slaves. Hard to imagine their giving that up without some violence.