Jenisha

The Jenisha are a Federation race with a troubled past. For ten thousand years, their world was plundered by a collection of other races, and their ancestors were taken as slaves. Eventually, they freed themselves through a series of rebellions, but soon became pirates and slavers themselves. Even after joining the Federation, they continued to practice slavery, but agreed to give it up after the Federation passed anti-enslavement laws. (TNG novel: Spartacus)