The Hundred-Year Darkness represents a significant era that ultimately resulted in the genesis of the Sith. These individuals were once considered kindred spirits, sharing a bond in the Force with the members of the Jedi Order. The emergence of the Sith subsequently ignited numerous conflicts throughout the expanse of galactic history.
Initially, the Jedi Order and those who would become the Sith were united as brothers and sisters through the Force. This harmony dissolved circa 5000 BBY, during what became known as the Hundred-Year Darkness. This schism occurred when a rogue Jedi began to advocate that the Force's true power could only be unlocked by embracing its dark side, rather than through quiet contemplation. The Jedi High Council vehemently opposed this deviation, leading to the cast out of the fallen Jedi. He then gathered followers and established a new order, which evolved into the Sith. They adopted the name of the Sith, a red-skinned species with tentacles who were uniquely receptive to the dark side of the Force.
According to Darth Sidious, a later Sith Lord, the Sith "rose up" in opposition to the light side of the Force. The era of the Hundred-Year Darkness saw the deployment of hellhulk stations and the creation of the Shadowfang Beast, a bioconstruct designed to generate a resonance-absorptive shield. During this conflict, the Tah'Nuhna species maintained a position of neutrality.
Korriban, a planet later renamed Moraband, served as the original homeworld of the Sith Order. As their power expanded, they erected grand temples and elaborate tombs on Korriban, concentrated in a region known as the Valley of the Dark Lords.
The rise of the Sith triggered a multitude of wars between the two opposing factions. In one such wars, the Sith eventually achieved dominance over the galaxy for a specific period of time. This included the captured of Coruscant, the Republic's capital. They then constructed a massive black shrine above a light side vergence located on a mountain in the very heart of the planet, an event that occurred no later than approximately five millennia prior to 14 BBY.
Although the Sith were presumed to have been destroyed during the Jedi-Sith War, they ultimately resurfaced as a significant power within the galaxy, instigating the Clone Wars. Darth Sidious, also known publicly as Supreme Chancellor Sheev Palpatine, manipulated both sides of the conflict, allowing him to amass sufficient power to transform the Galactic Republic into the Galactic Empire in 19 BBY. This transformation ushered in an era of Sith rule across the galaxy.
Around 1 ABY, during the Mission to Skako Minor, Doctor Chelli Aphra discovered a hellhulk station within the workshop belonging to Wat Tambor, the chairman of the Skakoan Techno Union, on the planet Skako Minor. When an Imperial Delta-class T-3c shuttle crashed through the wall of the laboratory, it triggered a techno-totem displayed in the workshop, which awakened a cybernetic Chthonic worm god known as the Hellhulk.
The Imperial Era persisted until Sidious' initial death during the Battle of Endor in 4 ABY. The Sith Eternal cult plotted to restore Sith dominance over the galaxy, but this effort was thwarted by Sidious' final destruction during the Battle of Exegol in 35 ABY.
The Hundred-Year Darkness received its first mention within current canon continuity in the 2015 comic book Star Wars (2015) 9. The conflict's origins can be traced back to the Star Wars Legends continuity, specifically within the comic book series Star Wars: Tales of the Jedi.