In the time of St. Patrick "British slave girl" was a unit of currency, equivelent to three cows.
FWIW, India, SE Asia, China and Japan all had slaves at different times in their history.
Then you can get into some interesting distinctions about what is slavery and what isn't. Serfdom, for instance, shades into slavery, and the word slavery itself covers a remarkable range of institutions.
In the glory period of the Ottoman Empire, for instance, the most powerful and wealthy men in the Empire, who ran the entire government and military (a distinction without much difference in the Empire) were the slaves of the Sultan.
Their descendants are known as "Redlegs".
If they're kin to me it must be back in Scotland, because my Scottish ancestor in the direct male line left Scotland in the 40s (1740s) one jump ahead of the sheriff. He was a MacGregor (basically the Scottish Mafia) and he changed his name to escape his past . . .
That's an interesting question -- would you rather be descended from a professional criminal, or a slave, or a slaveholder? I know I'm descended from Nos. 1 and 3 . . . and probably No. 2 as well, although I don't know exactly where . . .