The bible mentions specifically two ethnicities in the context of slavery--Israelites and Canaanites (see Leviticus 25:39-55). Israelites should be self-explanatory--it's the same people who the laws of the bible applied to. The treatment of them in the bible is not very slave-like by what we'd think of it. They can't be sold, are eventually freed, and it seems were mostly selling themselves into slavery. Biblical law essentially treats them as hired workers who are permanently hired.

The Canaanites are the other group who can be enslaved in a way recognizeable to us. Canaanites were a bunch of Levantine groups--strictly speaking, Israelites are a Canaanite sub-group. So outsiders in identity, but not geographically, and maybe not culturally.

So in short, there wouldn't be much of an ethnic distinction between slaves and their owners in the bible's worldview. There's no phenomenon of slave importation, they're the same ethnicity as the other people in the area.