The Rebellion is an alliance of nations and independent people lead by Angella and the Princess Alliance dedicated to freeing Etheria from The Horde. It is the protagonist group of the series. Note that it is not a resistance group; while some of its members are ex-Horde, almost none are from Horde-controlled lands (a rare example of a member who actually does rebel against the Horde is Adora). The origins of its name are hence unknown.
As for before Adora united The Rebellion, not much is known except for the fact that it dissolved almost 10 years before due to a destructive defeat on a battle with The Horde. After she united however, it had a hard beginning. Even with having Angella, most of the princesses and even the whole of Mystacor on their side, Frosta decided she would not unite them as she did not find it necessary, for her kingdom had not been reached by The Horde yet. However, after Princess Glimmer was kidnapped and her rescue brought Entrapta's supposed death, it was again dispersed. It was brought together again in the Battle of Bright Moon, after Frosta and the others came in to help Adora.
The original Rebellion was Bright Moon, Salineas, and others, including George, who is one of Bow's parents. After a grim defeat at the hands of the Horde and the presumed death of King Micah, the Rebellion was dissolved, which left the various Kingdom's to fend for themselves against the Horde and other threats.
The Rebellion started as Bright Moon, Bow, Spinnerella, and Netossa. They never tried to fight the Horde, and all the original Alliance members gave up and kept to their own kingdoms. Then, Glimmer's efforts came to include The Princess Alliance, Swift Wind, and Sea Hawk, rebooting the entire project.
The re-reformed Alliance re-joined The Rebellion and continued to resist The Horde. The discovered First One's holo-images, fought The Horde in the North, and made friends with George and Lance. They also learn more about the previous She-Ra
The Princess Alliance teams up, tenuously, with Shadow Weaver to fight Hordak. They learn more about She-Ra, the First Ones, and portal tech. They search The Crimson Waste, where they make friends and enemies while learning the terrible truth about Mara, The Horde, and Despondos. They also try to prevent the end of all reality, which was triggered by Hordak's portal machine.
The Alliance gathered together to honor Angella's memory and to witness Glimmer's coronation. Glimmer became increasingly stressed as everyone tried to distract her from her grieving process by involving her with the coronation preparations.
The Rebellion fought to stop Horde Prime from taking over Etheria and to free the rest of the universe from his tyrannical rule. Horde Prime sent his clone army to the planet's surface to make preparations for when he seizes the Heart of Etheria. Horde Prime then began turning most of the rebels into his soldiers by impeding chips into their necks, linking them to his hive mind. Catra and one of the Horde clones, named Wrong Hordak by Entrapta, also joined the side of the Rebellion. After a brutal final battle, the Rebellion stood victorious; all those who were chipped were set free, magic stored inside the heart was returned to the rest of Etheria, and She-Ra destroyed Horde Prime.
There is a short series of videos for The Rebellion to recruit new members for the alliance.
- Mystacor and it's leader, Castaspella, stayed out of the fight between the original Rebellion and the Horde, but under the new Rebellion Mystacor has allied with the princesses.
- In the book Island of Magical Creatures, many of the animals volunteered to join the Rebellion if needed.