Slave Liberation

Slavery is a bad thing, at least in this case, so lets liberate the slaves!

There are three ways to do this:
 * A: Rescue someone else's slaves, usually by force,
 * B: Free some slaves you already own or you bought specifically to free them.
 * C: Or the Slaves free themselves. This is the Supertrope of Gladiator Revolt.

Examples are sorted by type of Slave Liberation.

Slave Liberation is a likely result of Made a Slave, but if it's combined with Happiness in Slavery or Property of Love it easily devolve into Activist Fundamentalist Antics.

It rarely if ever happens that the slaves want to get full revenge by making their former master(s) their slave(s), probably because this isn't a story idealist authors like to write.

Anime and Manga

 * Fisher Tiger from One Piece started a campaign to end slavery after being Made a Slave during his journeys. His burning hatred of slavery surpassed his burning hatred of humans so much that he freed all the slaves he could find, regardless of race.

Comic Books

 * In the Elf Quest elf-troll war arc the Wolfriders free Greymung's trolls so they can help fight against Guttlekraw's trolls who enslaved them. (This dismays Two-Edge, who never dreamed that trolls would fight with elves against trolls.)

Film

 * Indiana Jones and the Temple of Doom. Indiana frees scores of children who were enslaved and forced to dig to find the Sankara stones.
 * Tarl does this in the film version of Gor. This is not at all complicated, since the films really doesn't have anything to do with the books they claim to be based on.
 * The first we see of Conan as an adult in the 2011 reboot of Conan the Barbarian is him leading a raid to liberate a bunch of slaves from some pirates. The fact that a solid chunk of the slaves are topless, nubile women is, of course, just a happy coincidence.

Literature

 * Robert Heinlein's Citizen of the Galaxy. In the Backstory, Colonel Baslim stormed a raider's compound and freed the crew of a Free Trader starship who had been captured to be made into slaves.
 * Honor Harrington: Many references are made to the Genetic Slave Trade throughout the books, with Honor having made a name for herself early in her career by capturing a large ship full of slaves and freeing them. The people responsible for the slavery, Manpower Unlimited, are a recurring minor foe who back various other organizations in attacks on the Manticorans and the Havenites. They also
 * The Adventures of Huckleberry Finn. Huck helps Jim escape, sometimes referred to as "stealing himself," and Jim has plans to make money and then go back & buy his family for their freedom.
 * Danaerys does this in A Song of Ice and Fire, mostly by overthrowing the slave holding cities. The unfortunate side effects are extensive. In Astapor, a tyrant known as Cleon takes over the city once she leaves, and reinstitutes slavery except with the former masters as slaves. Yunkai agrees to free them, but the moment she leaves starts up the practice again and starts preparing for war against her. Some of the slaves, particularly those trained in skilled occupations, actually had a better quality of life before they were free, and she's disturbed to learn that people are trying to sell themselves back into slavery. Famine results because of the war to free them, and because some places refuse to trade with them.
 * In The Roman Mysteries Flavia frees her slave girl, Nubia.
 * The freek Hork-Bajir in Animorphs regularly raided Yeerk projects to capture Hork-Bajir controllers and starve out the Yeerks inside them.

Live Action TV

 * Quantum Leap: Sam leaps into his own great-grandfather, who was a union officer in The American Civil War, and comes across a Southern Belle whose slave is secretly running a leg on the Underground Railroad, the (great?) grandfather of Martin Luther King Jr.

Real Life

 * Hariet Tubman
 * This is basically what the documentary The Dark Side of Chocolate hopes to accomplish for the many child slaves used in the cocoa industry.

Religion and Mythology

 * In The Bible, Moses & God use extreme force to coerce the Pharaoh to release the Hebrew slaves, up to and including killing every firstborn of the oppressors in the country. Despite all this, the Pharaoh keeps stubbornly refusing to the point where God basically stops giving him second chances and starts actively making the Pharaoh even stubborner, to get glory for Himself.
 * In the book of Philemon, Paul encourages the titular Philemon to free his slave Onesimus.
 * 1 Corinthians 7 says not to be anxious if you're a slave but get free if you can. It also says do not become a slave of man.
 * Jesus was sent to "proclaim freedom for the captives", among other things.

Tabletop RPG

 * Dungeons and Dragons Forgotten Realms setting. The Harpers try to free slaves whenever practical and possible. The supplement FOR4 The Code of the Harpers had a story about a Harper who freed a group of slaves from Thayan slavers.

Video Games

 * Morrowind have several situations where you can use violence to liberate some slaves. There's also a questline for a organization dedicated to rescuing slaves, although this questline doesn't go very far.
 * We later find out that emancipation came between Morrowind and Oblivion. Turns out that king in the Tribunal expansion decided that slavery really wasn't the way for a modern monarchical province of the Empire, and used the consequences of the events of Morrowind and Tribunal to destroy one of the major opponents to abolition and co-opt another.
 * In Slave Maker, the protagonist is portrayed as righteous when doing this to other slaveowners, while NPC:s are portrayed as Activist Fundamentalist Antics when doing this to the protagonist: Those other slaveowners are portrayed as truly abusive and in some cases monstrous, while the game keep waving a Consent Flag for the protagonist.
 * World of Warcraft have a lot of missions about rescuing slaves.
 * Wrath Of The Lich King: Mostly living people of all races forced to work in mines belonging to the undead scourge.
 * Cataclysm: Twightlight's Hammer is now the new faction that you generally rescue slaves from.
 * Fallout 2 and 3 are unique in that you can either help the slaves against their aggressors, or you can become the slaver and sell certain people off for caps.
 * See also Slave Revolt below.

Web Comics

 * In Order of the Stick, the order in general and the Haley & Elan duo in particular have taken up slave liberation sidequests. One of them ends... poorly.
 * In Spacetrawler, the main plot is a quest to liberate the Eebs.

Western Animation

 * Jonny Quest episode "Turu the Terrible''. Dr. Quest and Race Bannon kill the title pteranandon, freeing many natives who had been forced to mine for trinoxite ore.
 * Batman and Kamandi do this in the Batman the Brave And The Bold episode "Last Bat on Earth!".

Film

 * In A Funny Thing Happened on the Way to the Forum Pseudolus is freed by his master at the end for helping the son gain his bride.

Literature

 * In Uncle Tom's Cabin, the Decoy Protagonist is a kindly white man who decide to set his slaves free - but then die before he get around to it, and the slaves suffer terribly under their new owner.
 * In the third Gor novel, Priest-Kings of Gor, Tarl almost revolutionizes Gorean society to outlaw slavery... but doesn't quite get around to doing it. (Gor being Gor, Tarl eventually realizes that slavery is a good thing).
 * Discworld Golems have a unique system whereby the free ones collectively save up their wages to buy the one who are still owned their freedom.
 * At the end of the first book of The Stormlight Archive, Dalinar ends up  in order to free all of Sadeas' bridgemen.
 * In Guns Of The South, the first item on Robert E. Lee's agenda after being elected President of the Confederacy is the slow, gentle emancipation of all his country's slaves.

Manga and Anime

 * This prompts the Inevitable Tournament arc in Mahou Sensei Negima.

Video Games

 * Neverwinter Nights: Hordes of the underdark give you to buy a slave, you can free her by sending her with a message to your allies. Any other option results in her death.

Web Comics

 * Attempted by Flora of Two Kinds, who offers to let her human boyfriend Trace buy Keidran slaves in order to set them free... from someone who knows Trace can't afford them, even if he was selling.

Real Life

 * The Romans sometimes used to free slaves (manumission) and it became such a social institution that they developed a whole legal code around how it could be done, the legal status of a freed slave and his descendants and so on. Of course, their motivation was not a belief that slavery was wrong. Often manumission happened because it was possible for a slave to buy his own freedom from his savings, so it provided an incentive for them to work hard.
 * It helps to remember that if the Romans didn't see slavery as vile as we do, its at least partly because they viewed the institution in radically different ways than we do. To modern Americans, slavery is an exclusive, racialized matter; to the Romans(and other ancient peoples) it was something that could befall anybody. Or, to paraphrase a book on the subject: By modern standards of enslavement, Julius Freakin' Caesar was once enslaved for a time
 * Slaves in the southern US also could buy their freedom, given enough money. Some of them would even self-mutilate, to lower the price of their freedom.

Film

 * Spartacus

Literature

 * At least half of the Redwall books involve slavery, and when they do they will invariably be freed or rise up by themselves.
 * The first two free Hork-Bajir in Animorphs were runaways, prompted by the Ellimist
 * Honor Harrington again with the Verdant Vista/Torch rebellion. Overlaps with type 1, as it's a multinational effort involving people from Haven, Manticore, Erewhon, and the slaves themselves.

Video Games

 * The Fallout 3 DLC expansion "The Pitt" is based entirely around starting a slave revolt scenario by getting yourself enslaved and undermining the operation from within.
 * The premise of Lesbian Spider Queens of Mars is that the eponymous Queen's harem has launched a coup and she needs to web her girls back up again.
 * The backstory of Fire Emblem's Akaneia canon features this - during the rule of the Dolhr empire, a band of slaves led by a man named Iote revolted against their Dolhr masters, tamed the wild wyverns to use as mounts, and after the fall of Dolhr founded the kingdom of Macedon, with Iote as their first king.

Web Comics

 * In Overside, the short comic "The Tusks of Wusterim" shows that the kingdom of Wusterim was destroyed when its frog slaves revolted.

Real Life

 * The Arab world saw the Zanj Rebellion in 869, which was lead by an Ali ibn Muhammad who managed to take Basra. It took fourteen years to defeat them, and half a million people followed him. Most of them were East African slaves, but other people joined their fight.
 * Haiti is the only nation that was founded via a slave revolt. Well, the full story is more complicated: The Haitian Revolution was a thirteen-year long clusterfuck where the black slaves (about 90% of the population - most of them were even born in Africa, not Haiti), the mulattoes, the whites (themselves divided into monarchists and republicans) fought each other, and the states of France (first under the Jacobins, later under Napoleon Bonaparte), Britain and Spain interfered. Revolutionary France first gave human rights to free blacks and mulattoes in 1792, then abolished slavery officially in 1794 (to get the slaves defend Haiti against the invading Spanish and Brits), then Napoleon tried to re-introduce slavery, but his army was decimated by yellow fever... it's complicated.
 * Before the more famous Spartacus, there were two other big slave revolts in Ancient Rome. See here and here.