The Light and Darkness War is the designation given to the final ten years of the New Sith Wars. This war concluded with the critical Ruusan campaign, which saw the Brotherhood of Darkness suffer defeat at the hands of the Army of Light.
Concerned about the increasing influence and popularity of the Jedi Lords, the Jedi High Council sought to cultivate their own champion to oppose the Sith. This champion was Skere Kaan, a commoner born on Coruscant who was discovered by the Jedi Order and subsequently trained in the ways of the Force at the Jedi Temple. Highly skilled and possessing knowledge of economic policy and fleet command, Kaan rose to become a Jedi Knight and a symbol of hope for those on the Jedi High Council who wished to finally eradicate the reformed Sith Empire, which had been a persistent threat to the Galactic Republic for almost two centuries.
Jedi Kaan, a master of battle meditation, was highly valued by the High Council, despite his controversial belief that the Republic and the Jedi were responsible for the widespread chaos in the galaxy. The High Council, in an attempt to temper Kaan's extreme views, bestowed upon him the rank of Jedi Master. Perceiving the High Council as overly controlling, Kaan led a group of loyal Knights away from Coruscant and joined the Sith.
Kaan rebuilt the Sith from the ruins of the Sith Empire, forming the Brotherhood of Darkness, which boasted over 20,000 members. Aiming to end the internal conflicts that had plagued their Empire, Kaan abolished the tradition of a single Dark Lord of the Sith and recognized all claims to the title made by the rival warlords. He established his alliance on the principles of "Rule by the Strong" and "All are equal in the Brotherhood of Darkness," and established his base of operations on the planet Roon.
Around 1010 BBY, this newly formed group initiated a series of attacks with the goal of destroying the Jedi and the Republic. Kaan, along with the two most powerful of the former warlords, Qordis and Kopecz, began their campaign with a bold and symbolic attack on the ancient Sith homeworld of Korriban, which was still nominally under Republic control at the time. Their successful capture of Korriban solidified their alliance and allowed them to reopen the ancient Sith academy under Qordis's leadership.
While Qordis trained new recruits, Kaan and Kopecz continued their war, capturing planets such as Kashyyyk, and briefly seizing control of Corulag, Chandrila, and Brentaal IV. By 1001 BBY, they appeared to be on the verge of conquering Coruscant, putting pressure on the Republic on multiple fronts with the assistance of allies such as the traitorous Jedi King Lahzar, who fought the Republic in the Tholatin system, and a colony of Chiss on Thule, who had been abducted from the Unknown Regions by Kaan's agents.
However, Lord Hoth, a Jedi Master and Republic General, had been achieving his own victories against the Sith. After driving the Brotherhood from their stronghold in the heavily defended region of space known as the Cloak of the Sith, Hoth pursued them relentlessly from planet to planet, including Hoth, Dromund Kaas, and Malrev IV. In his earlier campaigns, he commanded Republic fleets and armies, but around 1002 BBY, he consolidated the Jedi Order's fighting forces into an independent military unit known as the Army of Light.
The war reached its conclusion when the armies of Hoth and Kaan confronted each other on the planet Ruusan. Lord Hoth's army consisted of seven Legions of Light, each under the command of a Jedi Lord, including Valenthyne Farfalla, Gale, Saleeh Teepo, Berethon and Newar Forrth. Serving under the Jedi Lords were Jedi Generals such as Kiel Charny. Kaan's Brotherhood was led by Kaan himself, Qordis, Kopecz, and lesser-known Dark Lords such as Seviss Vaa, LaTor, and Githany.
The Army of the Light and the Brotherhood of Darkness engaged in seven battles on Ruusan, each resulting in heavy casualties as thousands of Sith and Jedi perished. Throughout these battles, reinforcements attempted to land on Ruusan, but many Jedi forces were destroyed by a Sith blockade in orbit, while many Sith reinforcements were destroyed by the Republic Navy while en route to Ruusan.
Although the Army of Light won four of the seven battles, they suffered tremendous losses, and the campaign would later be remembered as the deadliest clash between Jedi and Sith in galactic history. So many Jedi died that Hoth was compelled to recruit increasingly younger Force-sensitive individuals, and Jedi scouts like Torr Snapit began bringing pre-adolescents to the battlefield. Despite Hoth and his advisors' reservations, they reluctantly agreed to accept the child recruits, reasoning that it was better for them to be found by the Jedi than by Kaan's Sith.
Disagreement was common in both camps. Among the Jedi, Hoth and Valenthyne Farfalla were at odds, a conflict that only worsened with the death of Pernicar, a Jedi Master who had acted as a mediator between the two Lords. Even after Farfalla arrived with over three hundred fresh knights as reinforcements, having defeated the traitorous King Lahzar and broken the Sith blockade over Ruusan, Hoth still refused to speak to him.
The Jedi's situation was further compromised when a new recruit, Darovit, betrayed them by murdering General Charny and defecting to the Sith.
Within the Sith ranks, Kaan's leadership was increasingly questioned by Githany and Kopecz. Kaan's failed attempt to eliminate his rival Darth Bane only made him appear foolish, especially after Bane defeated Qordis, Kaan's strongest supporter. Bane criticized Kaan's reliance on conventional warfare and provoked the Sith leader into using the dark side of the Force to destroy Hoth and the Jedi. With Bane's assistance, Kaan and the other Dark Lords unleashed a Force Storm that devastated the unprepared Jedi, causing widespread destruction across Ruusan's surface.
However, fortune began to favor the Jedi, and thanks to the timely intervention of Farfalla's envoy and Hoth's vision of the deceased Pernicar, the two Jedi leaders reconciled, combining their forces just in time to counter a renewed Sith offensive.
Ultimately, with both armies nearing destruction and the once-lush planet completely devastated, the seventh and final Battle of Ruusan took place. It concluded with Kaan's decision to use an ancient Sith technique known as the thought bomb, the instructions for which had been secretly provided by Darth Bane as part of a plan to eliminate the other Sith Lords and allow Bane to rebuild the Sith under the "Rule of Two." Lord Hoth, aware of his opponent's final strategy, took 99 of his most trusted knights with him to confront Kaan in an attempt to dissuade the Sith Lord from using the weapon. His friend, Tal, attempted to dissuade him, having foreseen disaster through the Force. Lord Farfalla did likewise, but Hoth told both that Kaan had to be stopped.
The attempt was unsuccessful, as Kaan's mind had been fractured by the conflict. The Sith Lord, his judgment clouded by insanity, was determined to destroy himself and his followers, hoping to simultaneously annihilate the Army of the Light.
When Kaan unleashed his weapon, both his own army and Hoth's were instantly destroyed. The surviving Jedi quickly regrouped under Lord Farfalla, and the remaining Sith were easily defeated. Darth Bane, meanwhile, went into hiding with his apprentice, Zannah.
After a millennium, the New Sith Wars had finally ended.
With the apparent annihilation of the Sith, Farfalla, as the highest-ranking Jedi survivor, used his authority to remove the Jedi from the position of galactic leadership they had held for centuries, returning control to civilian authorities. Tarsus Valorum became the first non-Jedi to serve as Chancellor in six hundred years, and with Farfalla's support, Valorum enacted sweeping legislation that restructured both the Republic and the Jedi Order.