It's somewhat bothersome that for thousands of year human societies practiced slavery throughout the world (from the wiki article on slavery: "Historically, slavery was institutionally recognized by most societies; in more recent times, slavery has been outlawed in all countries...").
It's tough to read things like Plato's 'Republic' and not question how brilliant individuals couldn't even fathom a society without slaves of some sort, even if they were treated well in an idealized utopia. I know that abolitionist movements have existed through much of recorded history as well, but I still don't quite understand why it took the last 6 or 7 centuries for these ideas to begin to take hold across Europe and the rest of the world.
Any help in figuring this out other than just saying "the Enlightenment" or "people got nicer" would be greatly appreciated. Looking for input a bit more complex than an ELI5 entry.
Slaves are very useful. They allowed people like the Ancient Greeks to maintain their quality of life and engage in pursuits like studying philosophy. This gave people a lot of reason to rationalize slavery. These rationalizations could be quite complex and convincing (to the people giving them). People were genuinely convinced that different types of people had different moral worth.
With the development of industry and technology the overall advantage of slavery was lessened which reduced the pressure to maintain the institution.
I think that people overplay the ideological aspect. Especially if people think that we "got nicer". Slaves were less economically viable which meant that people didn't care as much about keeping slavery around.
I know this isn't as in depth as it could be, but the economic aspect is something that gets overlooked too often.