It is a period of turmoil in the Galaxy. The fierce Mandalorian warrior race begins the MANDALORIAN WAR by viciously and simultaneously attacking three quadrants of Republic space. As the battle rages on, Jedi Master REVAN moves surreptitiously between unknown sectors, scouting for potential strongholds to withstand the attacks. He soon discovers the shadowy Malachor V, a planet listed by Mandalorian scholars as "forbidden" to step foot on. The reason for this soon becomes clear as Revan is almost devoured by primal Sith forces on the world's surface. Revan's will allows him to feed on (and not be consumed by) the power of the dark side. Revan develops an evil but brilliant plan: Using the dark power of Malachor V, he will seduce an army of Jedi, completely loyal to him alone. He will then turn the planet's evil power against the Mandalorian army in battle, luring them to his stronghold and destroying them completely. A stronghold is immediately constructed.
Meanwhile on Dantooine, the small Jedi academy overseen by Master Vodo-Siosk Baas is shocked to learn that a lone Jedi Padawan has disobeyed a direct order from Jedi Master ATRIS, a prominent Jedi on the Council. This single student has left behind the relative safety of the training grounds to fight alongside the Jedi loyal to Master Revan. But this young one, like the other Jedi brethren, is unaware of the tremendous dark side power wielded by Revan and the terrible secrets of Malachor V. Revan's power continues to grow, and he secretly strengthens his stronghold, hiding it even from his apprentice, DARTH MALAK. Soon, the evil force infecting the planet became the FORGE for Darth Revan's shock troops; the feared SITH ASSASSINS - fallen Jedi, tempted and cajoled by the evil of Malachor V, and under Revan's evil command. Soon, a shadow academy to the one on Korriban is constructed; and an evil enclave mirroring the Jedi academy on Dantooine is complete.
It is a period of tumult and astuteness for the galaxy's most powerful entities, as the Mandalorian conflict culminates. The Jedi, fighting alongside the Republic and their finest tactical minds, such as Admiral SAUL KARATH aboard his flagship Leviathan, begin to force the fierce Mandalorians back into a retreat. The rout of the Mandalorians reaches a crescendo above the skies of Malachor V. Unbeknownst to the Jedi Order, DARTH REVAN has discovered numerous Sith artifacts and holocrons, all stored in great tomb-like cities buried beneath Malachor V's surface. As Revan plundered these tombs and relics, he fell deeper into the Dark Side. He learned of the location and the true nature of Korriban, he learned of the location of other Sith artifacts, and he learned how those strong in the light side of the Force could be seduced and made to see the strength inherent in the Sith teachings.
Revan knew he had discovered more than a staging area for the Mandalorian War - he had discovered an ancient, planet-sized Sith storehouse of knowledge. He had discovered a world that held one purpose - to teach and train others in the ways of the Sith. He had discovered a weapon that he could use against the Mandalorians, and a weapon by which he could convert more Jedi to his cause. This process of "turning" Jedi into SITH ASSASSINS continued even as the Jedi Council hailed Revan as a hero, as he lead the Republic forces to victory over the Mandalorians in the skies above Malachor V, and forces them to surrender. Revan is able to draw upon the dark side energies of the planet below and use it during the battle, destroying the Mandalore and ending the Mandalorian threat. Simultaneously, more and more Jedi, unable to ignore the power emanating from the planet below, become corrupted by its influence.
A lone Jedi Knight, who had journeyed earlier to fight alongside Revan, forsakes him after the surrender of the Mandalorians - and the apparent loss of the Knight's connection to the Force during the battle - and journeys back to the Old Republic, determined not to fight any longer. The Knight is exiled by the Jedi Order, and the Knight's lightsaber is removed. Meanwhile, Darth Revan and his apprentice, DARTH MALAK, return from the Mandalorian War with a new fleet, comprising many previously loyal Republic soldiers and commanders, and a systematic and lethal attack begins. In tandem with the attacks of his fleet, Revan orders his SITH ASSASSINS to ratchet up the frequency and brutality of their swift attack strikes. The period of history known as the Old Republic Insurrection begins.
In disarray, the Jedi Council quickly gathers a small band of Jedi warriors together under the command of Jedi BASTILA SHAN with an imperative and almost suicidal mission; to capture Darth Revan, demoralize his troops, and strangle the insurrection. Setting a trap against a small Republic fleet, a small Jedi strike force boards Revan's ship, battling the Dark Lord into submission. Rather than helping his Master, DARTH MALAK lets the Jedi drag Revan from the throne after attempting a mind-wipe which was only partially successful. Returning to the Council with a comatose Revan, Jedi Masters healed Revan's mind, and implanted a loyal Republic personality.
The Feeding of Malachor V
It is a period of uncertainty across the galaxy. After a long and vicious battle in the deepest area of the STAR FORGE, Dark Lord of the Sith DARTH REVAN succeeds in destroying his ex-apprentice DARTH MALAK. After recovering from the duel, Revan seeks out the secret dark outposts he established during the Mandalorian War. Journeying to the Outer Rim in the EBON HAWK, Revan is focused with a single purpose: locating the source of the dark power on MALACHOR V. Those awaiting Revan's arrival, including members of the Sith and the Jedi, are shocked when he fails to return from this pilgrimage. It is unknown whether Revan destroyed or resurrected the primal Sith forces on this forbidden planetoid.
The turmoil of the previous decade has had a detrimental effect on the surviving members of the Jedi Order. Disillusionment and despair persists in the wake of the war both throughout the Old Republic, and within the Jedi Order itself. Furthering exacerbating the malaise is the corruption of Darth Revan and Darth Malak, and the untold harm their actions had brought to the Republic. These three reasons were cited by many the impetus for the disbanding of the Jedi. While the Jedi mull over their troubles, the battle-hardened Mandalorian hero CANDEROUS ORDO returns to the homeworld of DXUN, seeking to rebuild his clan, and find a new purpose in the galaxy. Through prowess and cunning, he rises to eventually become Mandalore.
JEDI MASTER KREIA, Revan's old mentor, is still haunted by guilt, wondering whether it was her teaching that resulted in Revan's fall to the dark side, and begins to search for him. Sensing his last location, she travels to Malachor V, but is unable to shield her emotions, and is completely consumed by the dark side of the Force. She is lost to the Jedi, spending the next several years on Malachor V, learning its secrets, and eventually becoming The master of the Sith academy there. Guided by Kreia's influence, Sith assassins once again begin to emerge silently from Malachor V and strike at isolated Jedi across the Republic, capturing some Jedi to turn to the dark side, and slaying those that resist. Taken to the dark side world of Malachor V to be fed to the planet's dark energies, these Jedi husks create even more assassins and DARK JEDI, feeding the planet's hunger.
~~Personal comments resume here~~
Now, I still have a few bones to pick with this version as well. "Revan's will allows him to feed on and not be consumed by the power of the dark side" and then the next sentence is the brillinant plan of 'Hey, let's conquer our own Republic!'
Which seems like a very corrupted dark side thing to do. There's just no way around that.
Like you said, I think the best explanation is basically wartime trauma. My personal version goes like this: (LSF!Revan personally so going to use she/her in this bit)
Revan is looking for tactics against the Mandalorians. The reason it was picked was because it was a taboo world to them. She wants to find out why and maybe use this to her advantage. Goes there, probably discovers the Trayus Academy and is horrified by this, especially since the world is opening up to settlers now. Decides to take two birds with one stone and defeat the Mandalorians there and get rid of this dark side nexus at the same time. (Jury's out on whether the temptation of knowledge is too strong and she Dabbles in some of the things there. Probably a strong possibility. Malak definitely does.)
Bao-Dur creates the Mass Shadow Generator, they have the big fight, but she screwed up and it worked better (worse?) than ever intended. Everyone gets a touch of void and it makes all the Jedi go mad and dark side, including Revan. And if you're going a bit mad, things like disappearing into the Unknown Regions become a bit more justifiable in the addled mess of her mind.
Especially, referencing another post here, that the Jedi didn't set a great track record of being welcoming and forgiving when they exiled the one Jedi who returned to them and covered up the true reason why. None of the Revanchists would have any reason to feel inclined to come home. At some point during the war, (referencing comics) just before the Covenant affair was exposed on Coruscant, some of the Jedi Council even put arrest warrants out on Revan and Malak. So they definitely weren't going to get the welcome mat back home.
To quote Bastila- "The dark side is not simply giving in to anger or temptation to use the Force to destructive ends. These things only lead to the dark side. The dark side grows stronger and more insidious the closer you draw to it. It begs you to surrender to it, to release all its terrible power⊠and it becomes harder and harder to resist. And once you stop resisting, it is too late. It twists you up inside and⊠and turns you into a mockery of everything you once stood for."
Invading the Republic they once protected is definitely a mockery of all that Revan and Malak once stood for. The dark side in itself is brainwashing enough, they didn't need help from any Sith Emperors.