Classical slavery was an answer to "what do we do with the people left over after conquest?"Of course, the transition to kings from judges in the Old Testament

Classical slavery was an answer to "what do we do with the people left over after conquest?"Of course, the transition to kings from judges in the Old Testament ( which I use because it's one of the few written artifacts left from then ) led to various prophets decrying the hubris of conquest. This hubris led to things like the Temple falling American Peculiar Institution slavery was a widening of the scope of Iron Triangle trade in the Carribean by rapacious Mercantilists. And to your last point, there's the line from "A Man For All Seasons" - "It'd give the Devil benefit of law for my own safety's sake."