Slavery is a moral wrong. And sadly it is a moral wrong that's rather constant throughout the whole history of mankind. That can be as a part of Triangle Trade in the plantations of the America's, Barbary raids on Europe's coast to capture oarsmen, the Indian Ocean slave trade or slavery in Korea. And then there's also "slavery adjacent" cases like serfdom which continued long into the 19th century in Eastern Europe. It's a coalecion of circumstances; technological innovation, innovation in economic thought and moral innovation from both the Enlightenment and Christian moralism that allowed for first the push to abolish the slave trade and then the practice itself. And these factors concentrated themselves enough in the Britain of the late 18th and early 19th century. A whole lot of devellopments in the history of man can be described as a coalecion of circumstances like this, but we do not not assign the credit where it is due in those cases. The economic incentive was ofcourse selfish as well, a free man is more productive thus his boss can earn more. But as the man is now free, earns a wage and is master of his own fate, it's a situation in which everybody gains something. Nothing of what I said should be taken as gloating, it's a sad subject after all, but some credit where credit is due.
As for my statements on the British Empire earlier in the post, I have recently been on a bit of a Old Brittania and Jackie Fisher roll on youtube. Fascinating subject. Drachinifel as well. My statement by quoting Kuyper is in regards to English/British strategy towards the Netherlands and especially Antwerp, as the one point from where an untouchable invasion of the island could be launched. Britain is forced to act on the continent when a (potential) hegemon takes controll of Antwerp and the Scheldt, a loaded barrel aimed straight at the heart of its Empire, London.
Edit: completely forgot about StrategyStuff's video on Julian Corbett (friend and ally of Fisher) as well.
My excuses if that was a bit rambly, but I hope it is sufficient