I think that some people used slavery as a means to an end. I mean FFS Great Britain abolished slavery in 1833 (I had to look it up; I new it was earlier) and they didn't even need a war to do it.
They ended slave-trading as well; Royal Navy ships were, well before the American Civil War, authorized to search any ship found on trade routes from Africa and search them for slaves. I believe they started this even before Britain actually made illegal the possession of slaves in their colonies, but I'd have to go look at it again.
Oh, great, you made me go look at it again
Legally it was not allowed for anyone to be enslaved
in Britain, and hadn't been since the year 1102. In 1722 a court case in Britain confirmed that people enslaved elsewhere could not be brought onto British soil and remain slaves, since slavery was, y'know, illegal. Finally in 1807 the slave trade was officially banned by Britain. True to Britain's present "we rule the ocean and therefore our word is law" stance, they didn't really specify that foreign ships were actually
exempt from this particular policy, and the British government would carefully look the other way when one of their ships boarded a foreign ship that happened to be carrying slaves. Also during the beginning of this period the British were more or less at war with
everyone thanks to Napoleon and company, and at the end of the war they forced basically everyone to agree to end the slave trade as well, leaving slavers with very few options for safe flags to fly to escape Royal Navy (And later other nations' ships) inspection.
Chattel slavery in most of the world was on the way out just because the British were the foremost naval power on the planet (And would be for another 100 years (until the very end of WWI, more or less) and they could singlehandedly stop the slave trade...and they did exactly that, at great cost and with no real benefits to themselves.
It's a cool bit of history.
Here's a video from Drachinifel concerning it.