Enslaved Elves

Basically, a once-proud and glorious race - doesn't have to be elves, but it usually is - have fallen. Usually, this happened before our story even began. Now, they live in squalor and slavery - those of them that still do live, anyway - with few traces of their ancient culture remaining. Perhaps, during the story, they will rediscover their old pride and power, for better or for worse... but only if the story's really idealistic.

Keep in mind that this trope only applies if there's some proof that the elves used to be a proud and noble race, before their 'fall'. If a universe's elves have always just been nomadic tribes of pointy-eared barbarian bowmen, it doesn't count for this trope, no matter how badly they're oppressed and see the violence Inherent in the System.

A subtrope of Screw You, Elves. Could be considered a kind of meta-revenge against Can't Argue with Elves.

Hopefully has nothing to do with Santa Claus or the Keebler company.

Examples of Enslaved Elves include:

Films

That´s a central point of the original Planet of the Apes and even stronger in its remake. And somehow, in the third and fourth sequel of the original you can argue that this trope appears in some way too.

Literature

In The Death Gate Cycle, the dwarves of the World of Air, Arianus, have devolved severely, losing their pride, and even their names. Calling themselves 'Gegs', they serve as peaceful factory-workers on the machine-filled island that is their home, worshiping visiting elves like Gods...
- ...that is, until one of the most peaceful and eccentric of their numbers inadvertently stumbles on the story's protagonist, Haplo, who had just entered their world. He ends up tagging along, seeing the rest of their world, and learning of the origin of the dwarves from Haplo. Later in the story, he returns to the Gegs, and leads them in casting off their elven lords. The twist from being an entire race of Comic Relief characters, to plunging their entire world into war and chaos (since the rest of the world is mostly reliant on the water produced by the Gegs' machine) is quite well-done.
The Magazine of Fantasy and Science Fiction ran a story, "An Elvish Sword of Great Antiquity" in which elves had been enslaved for a very long time, with obvious parallels with the enslavement of African-Americans and white attitudes towards them.
In The Witcher (at least in the books), Elves were once a noble and proud race, before humans came. At the time of the books humans threaten them, with parallels to European oppression of Native Americans in Real Life. And in last book we can see a proud clan that escaped to another dimension to escape the fate of their fellow elves.
- That proud clan of elves who escaped to another dimension butchered and enslaved the native humans there, instead.
In Michael Moorcock's Swords Trilogy, the Nhadragh race was once highly advanced in both magic and culture. By the time of the stories, they had declined to the point that they were conquered and used as slaves by the Mabden (humans).
In The Wonderful Wizard of Oz, the Munchkins were formerly slaves of the Witch of the East, and the Winkies and flying monkeys are slaves of the Witch of the West.
The Sithi from the Memory, Sorrow, and Thorn series effectively ruled the entire continent of Osten Ard until the humans came and warred upon them. The few remaining Sithi have isolated themselves from the rest of the world, and though they are not slaves, their race is a shadow of its former glory. The Big Bad of the series is a former Sithi prince who died in a war with the humans and now wishes to return to life.
The Nonmen from R Scott Bakker's Second Apocalypse series.
The terrifying Hork-Bajir from Animorphs were pacifist, ~~hunter~~-gatherer herbivores before being enslaved by the Yeerks.
This is hinted at with the house-elves in Harry Potter, as they are almost all slaves to wizarding families, yet possess powers and abilities that wizards do not.
Happens in JRR Tolkien's legendarium to the Noldor, though it's barely touched upon in the published The Silmarillion; The History of Middle Earth gives more details. Gwindor from The Children of Hurin was a Noldorin lord who was enslaved by Morgoth and forced to work in the forges of Angband.

Live Action Television

In Star Trek, in the evil alternate universe the Vulcans are slaves of the Federation's evil counterpart the Terran Empire.
- According to Star Trek: Deep Space Nine, this didn't last, with Spock becoming Emperor and all... Although that caused the entire Terran Empire to become slaves to the Cardassian-Klingon alliance (La Résistance rebuild the empire by 33 years after Deep Space 9, according to Star Trek Online.)
- The Bajorans were capable of stellar flight while humans were still learning to make fire, but are now an impoverished race that was sent back to almost an agrarian level by a brutal occupation.

Tabletop Games

This is one of the hallmarks of the Dark Sun campaign setting for Dungeons & Dragons. Overuse of magic has turned the world into a desert wasteland, leaving many of the races as pale shadows of their former selves. Dwarves no longer have their own lands and cities but do reasonably well among humans. Elves, are nomads and raiders. Halflings are savage cannibals. Gnomes are extinct.
In the updated adaptation of the original Dragonlance modules produced for TSR's 25th anniversary, the players can get some additional insight into what the evil green dragon Cyan Bloodbane really wants when he corrupts the elven kingdom of Silvanesti and turns it into a twisted nightmare. The heroes can meet a brood of illusionary green dragons who are being tended to by their elven slaves. The oldest dragon claims that Cyan is converting the forest back to the way it used to be when the green dragons ruled over it, before the elves rebelled and drove the dragons away. Now the dragons are returning things back to the "rightful" order of things.

Video Games

In Overlord, as well as its sequel, the elves are enslaved. In the first game, they had lost a war with the Dwarves, and most of them were killed, haunting the ruins of their old palaces as ghosts, while the survivors were forced to slave away in the dwarven mines. Depending on your choices, you could condemn the entire race to oblivion, by selling away the lives of the last remaining elf women, for a bit pile of gold...
- And yet, regardless of which choice you make, there are more elves appearing in the sequel - this time, they're enslaved by the anti-magic Imperium, forced to work in the empire's tourist-trap resorts. They've also got a hidden, underground city, but you'll take care of that minor problem during the course of the game, as well as crushing an uprising of the enslaved elves in the resort-city after you pillage and conquer it.
In Dragon Age: Origins, the Elves were once an advanced culture, and possessed immortality... Then humans showed up, and everything went straight to hell. By the time the game takes place, a few of the remaining elves live in savage, nomadic tribes in the deep woods, trying to keep the last few shreds of their culture alive - while the majority of them live amongst humans, where they're considered second-class citizens, relegated to slum-like 'Alienages', and mostly restricted to menial jobs such as being servants and messengers. However depending on decisions you make in the game, you can improve the situation for them, if only by a bit.
- Though the facts of their cultural prior to their enslavement are left intentionally vague, as most of their records and history were lost in the process. In particular, no one is quite sure if the whole 'immortality' thing is a fact, an exaggeration, or an outright myth. The only long-lived elf you meet in the game is thought to have regained their ancient immortality, but is actually tied to a magical curse that is keeping him alive. Similarly, it's said that Dalish elves have longer lifespans than elves who live among humans, but considering your lot in life when you're an elf among humans, there could be several different reasons for that.
In the backstory of Escape Velocity Nova, the Vell-os telepaths were at war for fifty years with the Colonial Council before the Vell-os surrendered to stop the bloodshed. The ensuing Carthaginian peace saw the Vell-os enslaved and their worlds blasted into space debris.
The vortigaunts from the Half Life series are race of wise telepaths and are generally more highly evolved than humans. They are first encountered as group of slaves under the mind control of another alien. In the later games, when they are freed, they join forces with humanity and regain their old culture. Their telepathic abilities make them valuable allies.
- ...as does their ability to shoot lightning.
In The Elder Scrolls series, the once-proud Dunmer (Dark Elves) have been largely driven out of their homeland of Morrowind by the time period Skyrim takes place in, after a natural disaster and an invasion by the previously enslaved Argonians. The Dunmer now live in slums as second class citizens in Nordic cities such as Windhelm.

Web Comics

In this Sluggy Freelance strip we see that the "Neebler" cookie elves have been slaves to the "Babisco" corporation since the company bought the tree they lived in with some shiny beads.
In Linburger, the Cyll used to be a highly advanced race with immortality and magic. Then something happened. Nobody in-universe is quite sure what went wrong. But now the Cyll are second class citizens, reduced to poverty and slums. They're no longer immortal, and so far they haven't shown an ability to do magic. The current generation doesn't even care about their past.

Web Original

In The Gamers Alliance, the Sarquil use dark-skinned desert elves, whom they have conquered in various wars, as slaves. The desert elves long for the freedom which the other elven cultures in the world have but are unable to do anything because even the Grand Alliance isn't willing to risk angering their much needed Sarquil allies by demanding the desert elves' freedom.