Etheria, the sister planet of Eternia, is ruled by Hordak, a tyrannical leader and member of the Evil Horde.
The Great Rebellion's greatest asset in their battle for freedom is She-Ra, He-Man's twin sister, who was previously a member of the Evil Horde, before defecting.
Etheria has often been linked to Eternia through the use of dimensional portals opened by
The Sorceress, are descendants of Eternian immigrant colonist.
At a glance Etheria appears to be a beautiful, lush, fantastical world. In reality, it is a dystopia plagued by the tyrannical rule of the Evil Horde, which invaded the planet long ago and conquered it.
Timeline of Etheria
Etheria was founded by a group of beings known only as The First Ones.
Their living spirits dwell in the Cavern of Fire, located in an underground kingdom, beneath The Crystal Castle. 
Cities and Towns Alwyn - a small village near the Hidden Forest.
Brigis Village - a village that was voluntarily put under a spell that keeps it prosperous forever, but makes it only appear on Etheria for one day each five hundred years.
Devlan - A small village similar in appearance to Thaymor, but more secluded.
Dryl - An industrial town near a profitable Etherium Mine. After the mine was run dry by the Evil Horde, they destroyed and burned down the village.
Colonia - A village that had it's food supplies confiscated by the Evil Horde.
Elberon - A town in or near Mystacor where Sorrowful, the dragon first emerged.
GaleBreath - A town whose members joined the rebellion after hearing Adora speak.
Glenmar - A village from which Horde Prime ordered all of it's inhabitants to be captured as slaves.
Greenfield - A farming village where at least one family gave up part of it's grain harvest to feed the Great Rebellion.
Green Thatch - A town overrun by Hordesmen and Thieves. Bow was once captured there.
Monstroid Central - Home base of the evil Monstroids.
North Land - A town where the Horde tried to start a re-education program where they burned books and taught children from a Horde-approved curriculum.
Octopus Cove - A Horde controlled port on the Sea of Sigh. It's controlled by Octavia.
Outpost Six - A Horde controlled outpost that includes an Inn.
Pinetown - A village situated between the Fright Zone and the Valley of the Lost.
Phlax - A village near which an Argonian Spaceship once crashlanded.
Rosewood - A farming community on which the Horde imposed heavy taxes.
Seaworthy - A Harbor town populated mostly by Sea Elves. It as one of Sea Hawk's Ports of call.
Small Oak - A town where Horde scientists invented a shrinking serum.
Thaymor - A town near or in the kingdom of Bright Moon. It is the town Prince Adam first went to when he came to Etheria. It was also one of the first places where She-Ra organized a rebellion. It was the home of the Laughing Swan Inn.
Castles and Kingdoms Bibbet Land - Home of the Bibbets.
Castle Blackmoor - Separated by Bright Moon by a swamp, this was the site of the Rebel's Fair, which celebrated the official start of the Great Rebellion. The Red Knight operated in this area.
Blue Mountain - Kingdom ruled by King Storm and his son Prince Highcliff.
Bluestone Palace - Although called a kingdom, the area around Bluestone palace is actually a protectorate of Mystacor and thereby ruled by Castaspella. The palace of Bluestone included a walled city.
Castle Bright Moon - A heavily fortified castle, which is the seat of power for a kingdom of the same name. It is ruled by Queen Angella, mother of Princess Glimmer. Queen Angella had magic powered by Etheria's two moons with which to defend the castle. This magic left the Castle vulnerable during eclipses.
Castle Condor - Home to Baron Condor and his men in Sand Valley.
Crystal Castle - The Castle is located at the top of Skydancer Mountain, and is also home to Light Hope. This is She-Ra's retreat, where she seeks advice whenever the Rebellion is in danger.
Kingdom of Darkedge - Home of King Jarod's Castle and the Crown of Knowledge
Darkspur Castle - Ruled by King Darkspur and located in the Hinderlands.
Dreer Keep - Home of Duke Dreer and situated in the Shadow Kingdom of Skull Path.
Elfworld - Ruled by King Varn and home to the Crystal Mines.
Erelandia - Commonly referred to as King Duplis' Kingdom, this kingdom payed taxes to the Horde, but Prince Hazar secretly helped the rebellion. He was sent to the Mines of Mondor on the planet Krytis for his crime. After his son was rescued by She-Ra, King Duplis agreed to help the rebellion.
Greenvale - an enclave kingdom within Mystacor made up of King Gruff and his blue furred leporidious species.
Halfmoon - Underground kingdom inhabited by the Magicats.
Kingdom of Highpoint - Home to Prince Norb and his men in Sand Valley.
Hidden Forest - Secret home of Alwyn the magician.
Mystacor - A magical kingdom ruled by Castaspella. The seat of power was a Castaspella's Enchanted Castle, which set atop a floating island. Many of its people are magically endowed. For a short time it was ruled by Mortella.
Mystacor Forest - A beautiful forest situated in Mystacor.
Nameless Volcano - On top of which Horror Hall is located.
Silverglade - A kingdom where a powerful Wizard lived, according to Broom.
Valley View Castle - a castle similar in appearance to Bluestone and Blackmoor.
Vargon - A Kingdom ruled by King Theymor and his son Prince Arkion.
Regions Beast Island - A dangerous jungle island that was seemingly made up mostly of rock and the fossilized skeletons of huge beasts. It was home to the Horde's main prison where it once held He-Man and the Dragon Sorrowful. Grizzlor was often in charge of the island.
Crimson Waste - A desolate place ruled by Scorpia from Scorpion Hill.
Dark Forest (also known as Darkside Forest) - an evil forest located in Mystacor when Mortella ruled the region.
Cave of Winds - a magical cave which can unleash unstoppable wind torrents.
Candor's Mountain - a stone mountain in Serenia that is home to Candor the Magician.
The Dark Mountains - A mountain range which contained energy mines. Horde slaves would often be taken there.
Flower Mountain - a place of great beauty where the Day of the Flowers is held.
Forbidden Zone - A dangerous part of Mystacor to which all it's evil was banned centuries ago by the Ancients.
Forest of Freedom - A beautiful forest that is home to Kowla.
The Freezing Mountains - Between the Whispering Woods and the Valley of the Lost. Possibly part of Frosta's kingdom.
The Fright Zone - The headquarters of the Evil Horde, home to their factory-like base. A large cloud of brownish smog covers the skies above.
Hinderlands - Ruled by King Darkspur from Darkspur Castle.
Hordak's Zoo - Built next to the Fright Zone, it is prison for animals surrounded by a moat filled with Snapgators.
Horde Base Camp - Located just outside Mystacor.
Lake of the Beastmonster - Located near old ruins, it houses the legendary Beastmonster.
Lavender Pond - pond where Bow and Adora were to meet each other once.
Moorstone - a region where the Evil Horde had an outpost overseen by Colonel Blast.
Nucleon Mines - Overseen by Ore Captain Sludge Man, here Horde slaves are forced to mine Nucleon.
Mystic Isle - an island where the First Ones once stored their greatest treasures such as paintings, arts and statues.
Mystic Stones - an area where Bow was once encouraged to take a vacation.
Salineas - underwater kingdom ruled by King Mercia of the Mer-folk.
Sand Valley - a desert area home to the Lowlands, Castle Condor and the Kingdom of Highpoint.
Scorpion Hill - Scorpia's base of operations in the Crimson Waste.
Serenia - a mystal place which houses the Balance Center of Etheria.
Skydancer Mountain - Crystal Castle sits on its summit.
Skyland - several floating islands inhabitted by Skylanders.
Spikeheart - A massive region of stone and mountains ruled by Agho, sorcerer king of the Trolls
Talon Mountain - A large catacombed mountain that serves as home and base territory to the Harpy race, lead by Hunga the Harpy.
Tomb Rock - A section in the Crimson Waste where Huntara once fought She-Ra.
Valley of the Lost - A desolate waste land where the ancient Library of the Valley of the Lost is located.
Woeful Mountain - Home to Noah the Wizard, who lives in a cave.
The Whispering Woods - The home of The Great Rebellion. An enchanted forest, protected from the Horde by a spell.
Seas, oceans and rivers
There are twelve oceans on the planet Etheria.
Crystal Falls - a peaceful place where Mermista can often be found.
Sea of Demons - On this sea the small Sea Elf town Seaworthy is banked.
Green River - used to be separated from Sand Valley by a range of mountains, but She-Ra rerouted the river to make it irrigate the harsh desert valley.
Growling Sea - According to legend, King Jarod was the first to hear the Growling Sea roar during a storm.
Polar Sea - The coldest of Etheria's twelve seas.
Sea of Sigh - Octopus Cove is a port on this sea.
Singing River - According to legend, King Jarod taught the Singing River how to sing when he as just a prince.
Crystal Castle ↑
The Stone in the Sword