I think there's a war about that wasn't there?

Yeah, and he didn't like the outcome. Salient quote (from a letter to Robert E. Lee):

"I saw in State Rights the only availing check upon the absolutism of the sovereign will, and secession filled me with hope, not as the destruction but as the redemption of Democracy. The institutions of your Republic have not exercised on the old world the salutary and liberating influence which ought to have belonged to them, by reason of those defects and abuses of principle which the Confederate Constitution was expressly and wisely calculated to remedy. I believed that the example of that great Reform would have blessed all the races of mankind by establishing true freedom purged of the native dangers and disorders of Republics. Therefore I deemed that you were fighting the battles of our liberty, our progress, and our civilization; and I mourn for the stake which was lost at Richmond more deeply than I rejoice over that which was saved at Waterloo. "

There are several lies in this. The objective of a Confederate victory was to enforce slavery farther south. Mexico was a few years away from collapsing. Brazil would emancipate within 20 years. Would the Confederacy last 20 years as the last slave state in the western hemisphere?

Slavery would not have lasted, as the mechanization and industrialization of agriculture would soon make slave ownership uneconomical. Same with draft animals.

Well, he wasn't wrong.

Whining about States rights to enslave people is certainly a take.

Particularly when in context, the war was caused by the South acting to usurp abolition in the North via the legal system (i.e. Dredd Scott https://en.wikipedia.org/wiki/Dred_Scott)

The importance and applicability of "states rights" is always oddly narrow.

    The importance and applicability of "states rights" is always oddly narrow.

It's also always ignoring the declarations of secession that all explicitly name slavery as the motivation.

The Confederate Constitution was mostly a copy of the US Constitution. One place where it differed is that it forbade any state from abolishing slavery. So the whole "states' rights" thing is obvious baloney.

Control of elections is one of the last bastions of State's rights. The past year has really illustrated why states' independence from the US federal government benefit their residents.

If you're familiar with English history, then it's more understandable that Lord Acton (Catholic, and born a mere Baronet) was against powerful central authorities.

And at least according to Wikipedia, Acton's positions on the Confederacy and slavery were very mainstream for English Catholics of the day.

    positions on [...] slavery were very mainstream

Thankfully we also had figures like John Brown to fight the good fight.

https://en.wikipedia.org/wiki/John_Brown_(abolitionist)

To clarify - John Brown was an American, with a Puritan/Calvinist background, born to fairly humble circumstances. Very unlike Acton.

And Britain's record on slavery is both far more complex, and far less bad, than many modern ideologues might have us believe. https://en.wikipedia.org/wiki/West_Africa_Squadron

He was pro powerful central authority, as long as that powerful central authority is pro-slavery.

He was against it when it prevented oppression.

Who is this "he" you are describing? Because your "he" bears minimal resemblance to the (extensively documented) Lord Acton.