"Either we win this war or the Sith will, what then will change?"
After nearly a thousand years of war, the Sith were in near-collapse—although the eleventh century BBY would later be described as the "Republic Dark Age", there is little evidence for any coherent Sith threat for much of the period. The Sith, though exponentially increased in number, were divided against one another, as the various warlords and self-proclaimed Dark Lords fought each other for supremacy. The Republic officially branded the war a "series of protracted military engagements" against an illegal organization but in reality the Sith were rampaging across the galaxy virtually unhindered, oppressing entire star systems.
The Republic, for its part, was a shrunken remnant, a pale shadow of what it once was. Much of its former territory was in the hands of independent Sith warlords who squabbled over the dying embers of the New Sith Empire. While they remained divided, the Republic was given some respite.
"Kaan turned away from the light and formed the Brotherhood of Darkness. The Brotherhood used the dark side of the Force to build an empire and were well on their way toward expanding it when an army was raised to oppose them. The army of opposition consisted of beings of many species and planets, representing all walks of life. But they had one thing in common. They were Jedi."
Out of the ashes of the New Sith Empire, a former Jedi Master, Lord Kaan, reorganized the Sith into the Brotherhood of Darkness, over 20,000 strong. In an attempt to end the intercine feuds that had torn their empire apart, Kaan ended the tradition of a sole Dark Lord of the Sith, and recognised each and every claim to the title by the rival warlords. Kaan forged his alliance with the creed of "Rule by the Strong" and "All are equal in the Brotherhood of Darkness". He made his headquarters on the planet Roon.
He became a Sith Lord, and eventually the Dark Lord of the Sith; known to his supporters as the "Dark One." At the time of Kaan's ascent, the New Sith Empire had fractured, with dozens of Sith Lords claiming the title of Dark Lord and waging endless campaigns against each other, rather than uniting to bring down the ailing Republic. Sensing that their endless quest for supremacy and power would destroy the Sith, Kaan set about reuniting the various splinter states under his banner.
"The forces who favor anarchy over structure have won. For what is this 'democracy' they speak of if not the absence of order? Of reason? Surely the strong should rule—for that is nature's way."
Kaan became the founder of the Sith army known as the Brotherhood of Darkness, and managed to turn it from a scrabble of feuding warlords into a powerful force to take control of the galaxy. The two most powerful Sith warlords—Kopecz and Qordis—pledged themselves to his cause, and they were followed by others, such as Kas'im, LaTor and Kaox Krul.
With his charisma and power, the Sith struck back at the Galactic Republic and the Jedi Order. Thousands of Sith and Jedi battled one another across the galaxy. Among the most notable opponents of the Sith was the aged Jedi Master Lord Hoth, who became a General with the Republic forces. Beginning around 1,010 BBY, this new group launched a series of attacks designed to destroy the Jedi and the Republic.
"This victory sends a message to the Republic and the Jedi. Now they will truly know and fear the Brotherhood."