[DiogenesLamp]

The plaque, erected by the Children of the Confederacy in 1959, reads in part '…the war between the states was not a rebellion, nor was its underlying cause to sustain slavery.'

That's because it wasn't a Rebellion, and the underlying cause was not to sustain slavery.

Slavery was already sustained, and would remain sustained so long as the Union followed the law.

I figured this article would be some bullsh*t like this.

[BroJoeK]

DiogenesLamp: "That's because it wasn't a Rebellion, and the underlying cause was not to sustain slavery."

Regardless of whether you admit there was any rebellion or not (a matter of semantics), the unimpeachable fact remains that on May 6, 1861 Confederates formally declared war against the United States.
That made it existential for the Union, not a war of choice.

DiogenesLamp: "Slavery was already sustained, and would remain sustained so long as the Union followed the law. "

Of course Lost Causers like to claim it wasn't "all about slavery", that tariffs or "money flows from Europe" were the really real reasons, but your problem is that's not what Confederates said at the time.
Sure a few mentioned other reasons, but first & foremost they complained about Republican opposition to slavery.
Here's the truth of it: every issue other than slavery was simply "politics as usual" in Washington.
Only abolition had the emotional power to drive otherwise loyal Americans to declare secession & war on the United States.

So, bottom line: DiogenesLamp's claim that secession was not driven by slavery is also a claim that Confederates themselves were liars.