Over the centuries and millennia a huge number of people have been slaves. Sometimes they were slaves of people who looked like them, some of these even being people they were related to or otherwise had a seemingly positive relationship with before hand. Sometimes they were slaves of people who didn’t look like them. Slaves came from all parts of the globe and most if not all nations over time and they could and did look like anyone since physical appearance of slaves was only one potential factor in why people might take them as slaves.
They might have become slaves after being kidnapped or they might have become slaves as prisoners of war or criminals sentenced for a crime. They could have been debtors who were unable to pay for something they owed. And some people did choose to become a slave for various reasons, although choosing to be an indentured servant when an option was more common than just choosing to be a slave for life.
They might have been born slaves or they might have become slaves later in life. Those born slaves might have lived their entire lives as slaves or they might have gained their freedom later in life.
How they were treated also vastly differed. Some treated them as fellow human beings who they happened to be responsible for taking care of while some saw them as objects to be used and discarded as they saw fit. The idea of one person owning another no matter how well they are treated does not sit well with me, but that doesn’t change the fact that it has been around for a very long time and at various points in time it was an accepted part of society.
Depending on your story it might make sense to include slavery. You might want to tell the story of someone who was a slave. You might want to have characters who have grown up with it as a normal part of life. You might want to show how slavery was ended. It is a difficult topic and maybe it isn’t something you want to include in your stories, but if you do have slaves in your story a situation like this might be something that arrives.
I’ll not ask what you think of slavery in real life, but instead when do you think it might be an effective tool in a fictional setting and how do you think it should be used in said fictional setting?