The Legion War or Great Legion War is a battle that spanned most of the galaxy, raging for 190 years, from 50 AD to 240 AD.
After colonizing most of the known galaxy at the time, the Golden Alliance began plans on how to terraform the uninhabitable planets they came across, in order to make them livable. This is when the BioGalactica corporation came forth with the Galactic Seed Initiative. A small, football-sized ball of slime would be shot onto a planet and, with its reconstructive nanites, spread across the entire landscape, transforming the environment into a beautiful, lush world. This was put into action immediately, and ended up having a 99.9% success rate. However, due to a clerical error buried under a mound of paperwork, one seed was mistakenly fired at an already inhabited, Watcher-Protected Planet. The pod containing the seed was far too small for the Watchers' radar to pick it up, and it arrived in a suburban neighborhood. Upon arriving, it scanned the less-than-tidy environment, concluding that Human were the source of the pollution, and that one nearby was compatible. This man's name was Alton, and the seed immediately jumped on him, filling his body with its own nanites. Over the course of the next few weeks, Alton was slowly transformed, and as a result of his idea of beauty, mixed with the seed's mahoutechnological programming to create beauty, he became Queen Althea, the first of the True Legion.
Althea shut herself off from most social situations, but after getting into a fight, she noticed her new latent ability to transform others. The problem being that those transformed by her new changing touch became mindless, loyal drones. She continued to slowly terraform in order to satiate her own Environmental Imperative, but eventually, she mistakenly transformed her best friend, Maya. Heartbroken by the loss of her most supportive friend, she sent her away to die. From this point on, Althea gave in to the Imperative, hoping it would teach her a way to ensure the souls of her converts were maintained. Not long after this, she and her recruits began work on the planet's hive tree, and soon invented the Vault of Souls. While new converts still remained mindless drones, they at least weren't gone forever. But Althea was already lost in a terraforming trance, and managed to conquer her entire planet in just six short months.
While that might have been the end of the war, it was only the beginning, as her daughters found the pod that contained the original Galactic Seed. Inside of the pod was a beacon that, when activated, would send a spaceship. This was likely the result of a contest, to see who could find the impact zone first, but through this ship, Althea's biotechnicians were able to reverse-engineer its biowarp drives and design their own solar-powered Legion ships. This allowed the Legion to start conquering other planets, and around this time, Althea developed the Legion Seed, much like the original Galactic Seed, only made out of pure Legion nanites, and colored pink. Unlike the other seed, this one was designed with the sole intent of creating new Legion Queens. In addition, Althea took note of the DNA the Legion memorized after converting someone, and created the Consort facet, allowing them to take the appearance of any race they've converted, even emulating a person down to their original appearance. From this point, the Legion tactics involved seeding a planet and awaiting the new Queen to convert enough consorts to infiltrate a secure area and take out the planet's military force before it even takes notice of them.
But with planets falling one by one to the Legion, the Golden Alliance soon took notice, and eventually subterfuge wasn't enough to continue their conquest, so the true war began. The GA and Legion fought over and over, and each time, the Legion's numbers would grow. Worse yet, if one of them fell in battle, a Renewer could dedicate time to the Legion Ritual of Rebirth, using their own body to gestate a new fetus with the same memories as the original body.
Over time, the GA grew desperate, and turned to the elders of the Dark Elves. They struck a deal, and generations upon generations of Dark Elves were sold to the GA in slavery. In one particular battle, the owner of the Marcus Materiel Corporation, Max Marcus III, lost his son Max Marcus IV as he valiantly fought back a Legion horde, allowing enough time for his unit to escape. Max watched over the security footage of the event over a hundred times, and became convinced that his son would have emerged victorious if only his equipment was better. From here, Max dedicated his company to developing super-weapons for the GA, including a pollution bomb used to ravage a world just to slow the Legion down.
While countless battles were fought during the war, one such battle involved the Castaway, a huge ship operated by Orpheus Ardentblade, a High Elf from the GA's high council. He gathered renown for his incredible valor and, in an age of hatred, filling his ship with mostly "Sub-Mythic" crew. In the Castaway's ultimate battle, it destroyed a Legion hive from orbit with an experimental laser cannon, and the crew sang Ardentblade's praises. He was elected to be a new leader of the GA, until the crew of the Castaway suddenly mutinied and came out against him, revealing that he had tricked one certain Dark Elf, Alyanna Fenris, into signing on with a condition that she would have several generations taken off of her family's slavery contract. However, after she was taken in, she was drugged up and hooked into the Castaway's biowarp core, constantly wracked with pain in order to release magical energy as a racial defense measure. In addition, Orpheus commanded most of his crew to fight on the ground before launching the laser bombardment, killing most of them in the process. Upon realizing this, the crew began to form a mutiny, but Ardentblade had Fenris cast a spell over the crew, altering their memories to paint him as a hero. Over time, she grew resistant to the drugs used on her, and managed to reverse the spell, having Ardentblade sent to a tribunal. But before he was set to show up, he mysteriously disappeared and the Castaway was sabotaged with Fenris still aboard it.
Meanwhile, the Legion had just managed to break through the Gate Cluster and enter Angelic Protectorate space, conquering a few planets on the outskirts. The AP developed a plan, and the Norse Elementals broke off pieces of three of their planets, forming the massive battleship, Yggdrasil. This began the AP's final battle with Legion, known as Ragnarok, and in the end, the Norse gods sacrificed themselves to seal the gate cluster, cutting off the local Legion Queens from their hive. This is thought to be one of the key factors in ending the war.
While it seemed like the war would rage forever, and the GA were slowly losing, in 240 AD, the Legion suddenly surrendered en masse, apologizing profusely as they all reverted to their previous personalities. Queen Althea had disappeared, and disconnected herself from the hive, freeing Legion all across the galaxy from her control. As an act of repentance, the Legion gave away most of the planets they had conquered and returned to their own small corner of the galaxy, where they remain today. Many have tried to return to their families, but due to propaganda spread by the GA, saying that once converted, they were gone forever, most were turned away. While most factions know to leave Legion alone, some theorize that Althea has just gone into hiding, waiting to reappear and resume her conquest when the galaxy least expects it.
In reality, a certain Mind Mage had made his way to Queen Althea, knowing she had already converted his true love. He made a case that he would join them willingly as long as he could stay by her side. She accepted graciously, but while he was being converted, he cast a powerful mind delve spell on the Queen, reaching into her deepest subconscious to find the soul of his beloved. Reaching through the hive was arduous, to the point where he forgot his own name in the process, but he eventually found her soul. But deeper still, he heard a calling out, and continued to reach deeper into the hive. Eventually he emerged, returning both his lover's soul, and Althea's. Lucid for the first time in nearly 200 years, Althea immediately ordered a ceasefire, and left one final gift: the Recruiter facet, to allow Legion to convert others willingly for the first time. After this, she disconnected herself from the hive, and launched herself into a cold, dark place of the galaxy, ashamed of all she had done. It's believed she starved to death, deprived of nutrients and sunlight.