Slavery

Slavery is the act of one sentient being controlling another in violation of the other's will. The one so controlled is referred to as a slave.

The Slaver Empire controlled a large galactic empire a billion years ago. The Slavers were known as the masters of all intelligent beings in most of the galaxy until one race revolted. (TAS: "The Slaver Weapon")

During the 19th century, a Skagaran ship was sent to Earth. The vessel's crew abducted several thousand Humans that were taken to help the Skagarans start a colony, and serve as slave workers. (ENT: "North Star")

In 1937 the Briori kidnapped 300 Humans from Earth and took them back to an unnamed Class L planet in the Delta Quadrant and used them as slaves. (VOY: "The 37's")

In 2153 a humanoid named Zjod traded in sex slaves of various species from a shop in a floating bazaar on the Xanthan homeworld. (ENT: "Rajiin")

The Orions used slave labor as late as the 23rd century. Common belief was that Orion women were slaves to the men, when it was in fact the opposite. In the 22nd century, Orions frequently kidnapped members of other species for slave trade. (ENT: "Borderland", "Bound")

During the Occupation of Bajor, 2328 to 2369, enforced labor was practiced at labor camps. This is a situation similar to slavery. (DS9: "Emissary")

The Kazon were a subjugated race, used as slave labor by the Trabe who had conquered their homeworld. They remained in captivity until in 2346, when Jal Sankur convinced the various Kazon sects to put aside their differences and rise up against the Trabe. In doing so the Kazon took the Trabe's ships and technology and forcing them to become a nomadic species, never allowing them to settle on a new world. (VOY: "Alliances")

When Bruce Maddox wanted to disassemble Data in 2365 in order to learn how to create more androids, Jean-Luc Picard considered Data's rights but failed to see the bigger picture. Guinan helped him realize that creating an entire "race" of Datas for use as tools would, in fact, be slavery. (TNG: "The Measure Of A Man")

The scene where Whoopi Goldberg's character Guinan infers that a series of Data-like androids would become slaves was particularly poignant because Goldberg is of African descent, and has appeared in films about the horrors of African-American enslavement.

In 2366 two Breen warships attacked the Ravinok, a Cardassian prison transport carrying 32 Bajoran prisoners crewed by 18 Cardassians. They forced that ship to crashland on the planet Dozaria. The Breen then used the survivors of this crash as laborers at a nearby dilithium mine. They remained slaves until freed by Major Kira Nerys and legate Dukat in 2372. (DS9: "Indiscretion")

In the mid-2370s, the United Federation of Planets began using sentient holoprograms, the various types of outdated Emergency Medical Holograms, for slave labor purposes, utilizing them for difficult and dangerous tasks such as warp conduit maintenance and dilithium mining. The publication of the holonovel Photons Be Free by The Doctor, however, caused many in the Federation to begin changing their minds about this practice. (VOY: "Life Line", "Author, Author")