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The Reformists, also known as the Reformers, were a faction of San'Shyuum, and fought with the Stoics during the San'Shyuum Schism. They wished to use the Forerunner Dreadnought to advance San'Shyuum technology.
The Reformists wished to enter the Forerunner Dreadnought and use its technological secrets, but the Stoics declared such actions to be blasphemous and heretical. The Reformists became technologically obsessed and desired to investigate the keyship to learn more about the universe. The difference in opinion between the two factions eventually culminated to the San'Shyuum Schism. During the civil war, the Reformists established a stronghold in the fortress of Granduin in the Zelfiss region. However, the fortress was undermined by Stoic forces and the fortress fell into the nearby sea—the Great Apothtea. During the climax of the San'Shyuum civil war, around one thousand Reformists stormed the Dreadnought and began to occupy it, while preparing to use the vessel to leave Janjur Qom. The Reformists occasionally raided Stoic territory to collect and stock the ship with plants, wood, seeds, and other goods from the planet.
Eventually, the Reformists commandeered the Forerunner Dreadnought and managed to escape Janjur Qom, blasting a huge chunk out of the planet in the process. The Stoics were unwilling to fire upon the object of their reverence, and grudgingly allowed the Reformists to leave. The Reformists ultimately won the San'Shyuum Schism, but it came with a heavy price. The Reformists were left with around one thousand individuals, and were forced to selectively breed to prevent inbreeding. The Roll of Celibates was established in an effort to maintain genetic diversity between the San'Shyuum and to eliminate unwanted genes. With the help of the Forerunner technology from the Dreadnought, the Reformists were able to survive and travel the galaxy.
The Reformists would later go on to encounter the ancient Sangheili in 938 BCE. Landing on the Sangheili frontier colony world of Ulgethon, the Reformists sent a large delegation to explain that they worshipped the Forerunners. However, the Sangheili, like the Stoics, deemed the use of Forerunner technology as heretical. An Arbiter met with the delegation and decapitated all of the San'Shyuum. Outraged, the Reformists left the world and the San'Shyuum-Sangheili War began. The Reformists were outnumbered by the Sangheili, but the Sangheili possessed inferior technology. This situation led to a stalemate between the two species. Eventually, realizing that both species' extinction was a possible outcome, the Writ of Union was signed between the San'Shyuum Reformists and the Sangheili and a religious empire known as the Covenant was established.
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