Post war group of propagandists is a pretty good way to put it.
They were responsible for many of the Confederate statues, and a lot of revisionist rhetoric has its seeds with them.
To be clear, they were effective. And the public school system still bears their mark today, actually it’s probably getting worse.
The South seceded out of fears of abolition. Full stop. Losing the election in a landslide to a Republican was only the last in a huge pile of straws. Ft Sumpter wasn’t even where the fighting started. People had been literally killing each other over the issue of continued/expanded slavery for several years already.
Any source claiming that the South had more nuanced reasons for leaving is either knowingly lying, or has been taken in by a lie.