Slavery

Slavery is the forced servitude of another being.

Human slavery
Humans were known to practice slavery on orcs and ogres after the events of the Second War. Blackmoore himself enslaved Thrall, the future warchief of the Horde. The king of Lordaeron was aware of Blackmoore's gladiatorial games and allowed them personally, as long as the royal coffers would see the proper percentage of his earnings. The enslavement of orcs has been practiced among the internment camps, Lorin Remka keeping Greekik as her own personal slave while Lord Agrovane bought Rehgar and used him as his gladiator. After the events of the Third War, few cases of humans using slaves remain. In the fallen kingdom of Alterac, Aliden Perenolde believed in slavery and sought to place the orc race back into chains — to return, in fact, to the days of Alliance internment camps under Aedelas Blackmoore.

Aiden Perenolde and later his son Aliden Perenolde planned to take the orcs as slaves.

It is possible that Bizmo's Brawlpub is still an underground example of forced gladiatorial combat (at least for some of the combatants) going on in Stormwind. According to Thrall, the Alliance and the kingdom of Stormwind still practice slavery. However, this may be an exaggeration elicited by Thrall's past experiences with the orc internment camps that were ran by humans.

The Kul Tiran house of Ashvane force their workers into exhaustion,  and also employ child labour by snatching children off the streets of Boralus then deporting them to the Ashvane Foundry. It is said that Kul Tiran slavers would blush before the depravity of a mogu slaver by the name of Zheng. At Redrock Harbor in Vol'dun, the Ashvane Trading Company enslave vulpera to work in the Redrock Mines.

Orcish slavery
The practice of slavery has historically existed in orc society, and while in modern times it seems to occur less, the practice still continues among the orcs, though it is unclear how widespread it is. Despite Thrall's work to ensure that no orc would be cast into slavery ever again, a small number of orcs have been found enslaved by other orcs in the Horde, for example Bloodeye Redfist. It appears that some orcs are also willing to enslave members of other races, both Horde and Alliance. Many of these slaves were however once criminals whom were brought to justice. It is unclear why the orcs still allow slavery, and to what extent, or why they choose to ignore it.

Okrilla at Dreadmaul Hold in the Blasted Lands, enslaved some of the ogres of the Dreadmaul tribe after recapturing the old orc city.

Ogre slavery
Ogres captured various races to labor in mines and fight in arenas.

Zandalari trolls
The Zandalari are above the use of slaves, they're strong and capable of seeing to themselves. Even the sight of slavery within their city is insulting to them. Additionally, they see it as a sign of weakness, and as such when they met the mogu–who built their empire with slaves–over 12,000 years ago, they saw themselves above the slavers.

Though for some reason, years after the Sundering over 10,000 years ago, a number of Zandalari came to Kezan and after some time ended up enslaving the goblins there. Why they did so is unknown, as it was against the Zandalari's beliefs.

Jungle trolls
Zanzil, an infamous witch doctor exiled from the Gurubashi tribe was known for his mind-bending concoctions that when ingested, turned the imbiber into a mindslave. He didn't care about who or what drank his mind-altering potions as the mindslaves under his control range all the way from jungle trolls and dire trolls to naga and ghouls.

During Zul's pledge to aid the Gurubashi back to greatness, Zanzil set out to attack both Hardwrench Hideaway and Explorers' League Digsite in the Cape of Stranglethorn, poisoning their food and turning goblins and dwarves into voodoo zombies.

Other examples of slavery

 * Warlocks do enslave demons, binding them to their will.
 * The naga have enslaved murlocs and broken as well as vrykul with merciless ones.
 * Goblin Trade Princes have enslaved trolls for mining, although they seek to keep this low key.
 * The mogu enslaved the pandaren and the saurok.
 * Elemental along with their Elemental Lords were enslaved by the armies of the Black Empire.
 * Ragnaros the Firelord has enslaved the dark iron dwarves.
 * The dark iron dwarves utilized slavery.
 * Demons have enslaved creatures by corrupting them such as orcs.
 * On Argus the Legion use Broken as slave labor.
 * The undead of the Scourge can be seen as enslaved spirits. Furthermore, in the Pit of Saron, several slaves are forced to work on saronite.
 * The blood elf tailors of Silvermoon use slave leper gnomes for work.
 * The Forsaken captured the villagers of Emberstone and used them as slaves.
 * Gerard Abernathy made Theresa his mindslave by lobotomizing her brain.
 * Twilight's Hammer cult had slaves.
 * During the war on the alternate Draenor, the orcs of the Iron Horde and their ogre allies of the Gorian Empire enslaved draenei and arakkoa.
 * The sethrak of Vol'dun are known to enslave vulpera and tortollans. In the Slithering Gulch, there are three slave markets that were burned by the Horde adventurer helping the Voldunai.
 * During N'Zoth's Assaults, the Amathet tol'vir enslaved the Ramkahen tol'vir in Uldum.
 * The Northsea Freebooters under "Mad" Jonah Sterling tried to sell the tuskarr as slaves when they die days after leaving the climate of Northrend, leading to disastrous results.
 * Kobolds are frequently enslaved by gnolls, who force the rat-like humanoids into an existence of neverending drudgery. Since their enslavement, the historically meek kobolds have grown bitter and aggressive toward any creature that meddles with their ceaseless labor. During the Alliance-Horde war, the Boulderslide kobolds of Stonetalon Mountains were subjugated by Horde forces to counter the Alliance-Grimtotem tribe partnership in the area. Kobolds themselves are not against enslaving others, as the Tunnel Rats did to a large group of troggs in the Silver Stream Mine.

Slavers / slave masters and slavedrivers

 * Aedelas Blackmoore
 * Lorin Remka
 * Aliden Perenolde
 * Rehgar Earthfury
 * Lord Agrovane
 * Slave Master
 * Kritok
 * Dark Iron Slaver
 * Thurg the Slave Lord
 * Ronag the Slave Driver
 * Slave Master Blackheart
 * Slave Watcher Crushto
 * Slave Hunter Mol
 * Slave Hunter Brol
 * Slave Hunter Krag
 * Shan'ze Slaver - Isle of Thunder
 * Coilfang Slavemaster
 * Bloodscale Slavedriver
 * Forsaken Slavedriver
 * Twilight Slavedriver
 * Shadowmoon Enslaver
 * Shadowmoon Enslaver
 * Zanzil the Outcast
 * Gerard Abernathy
 * Spiketooth
 * Subjugator Devo
 * Foreman Sharpsneer
 * Tunnel Rat Geomancer

Slavers are wealthy merchants who sell slaves. Goblin slavers, obviously, run Kezan's slave rings, or simply own several slaves of their own for personal use. Although the trade princes condone slave rings, the slavery trade is kept quiet. Goblins have no wish to offend potential customers who might object to this controversial but highly lucrative line of business.

Slaves

 * Mur'gul Slave
 * Centaur Drudge

In a lot of cases, enslaved mobs will rebel against their masters once the nearby slavedriver/slavemaster is killed.
 * Ravenclaw Slave - Silverpine Forest
 * Elemental Slave - Alterac Mountains
 * Sandfury Slave - Zul'Farrak
 * Slave Worker - Searing Gorge
 * Slave - Blackrock Depths
 * Voodoo Slave - Zul'Gurub
 * Wrekt Slave - Zangarmarsh
 * Wastewalker Slave - Slave Pens
 * Dreghood Slave - Steamvaults
 * Slavering Slave - Blade's Edge Mountains
 * Greengill Slave - Isle of Quel'Danas
 * Saronite Mine Slave - Icecrown
 * Skeletal Slave - Pit of Saron
 * Alliance Slave - Pit of Saron
 * Horde Slave - Pit of Saron
 * Troll Slave - Kezan
 * Bellows Slave - Blackrock Caverns
 * Farmstead Slave - Kun-Lai Summit
 * Troubled Slave Spirit - Krasarang Wilds
 * Saurok Slave - Isle of Thunder
 * Frostwolf Slave - Frostfire Ridge
 * Enslaved Tol'vir - Uldum

Slave camps

 * Slag Pit - Searing Gorge
 * Slave Pens - Zangarmarsh
 * Pit of Saron - Icecrown
 * Slave Pits - Lost Isles
 * Bloodmaul Slag Mines - Frostfire Ridge
 * Hatecoil Slave Pen - Azsuna
 * Slave Enclave - Highmountain
 * Deepsea Slave Pen - Nazjatar

Trivia

 * In Warcraft: Orcs & Humans, slave is the "lowest" rank you can achieve. In Warcraft II: Tides of Darkness it still is for Horde players, as the lowest Alliance rank is servant instead.