Fragmentation
A series of rebellions plagued the Black Legions in the ninth year of the war. As the Republic swallowed up more and more space, systems left the confederation and submitted themselves to the yoke of the Republic while others used the opportunity to sue for some form of sovereignty.
At this stage, one of the pressing concerns of the Dark Jedi was the Star Forge itself. Throughout the war, they kept its location a tightly guarded secret. This secret was easy to keep as they controlled all hyperlanes leading to and from it, but as the Republic expanded, these lanes fell into enemy hands. At this point, the only real defense the Star Forge had was its location in the Unknown Regions. Although the Republic controlled the bases of these hyperspace routes, they could not head inwards into the Unknown Regions as they did not know how to safely navigate these regions.
However, one of the Star Forge's greatest vulnerabilities was its hyperspace beacon. Remember, in this era hyperspace navicomputers with the preset data and computing power necessary to calculate hyperspace routes was not reliable or common. As a result, almost everybody, including military vessels, used hyperspace beacons to navigate. These beacons emitted pulses of hyperwaves or subspace waves that could be picked up by nearby ships. The ships computers would then use the data transmitted, the doppler effect, and any data gained from gravitational interference to triangulate the location of the beacon and the safest route to and from. These beacons could of course be tampered with, and many times in history enemy fleets were bamboozled when the enemy messed with a seemingly stable hyperspace beacon, but in order to be used by one side, it had to transmit accurate information, which could also be used by the enemy.
Now to get to the Star Forge, a beacon was necessary. Although Republic codebreakers did not know its exact location, their listening devices could pick up faint signals originating from the Unknown Regions. This, in itself, was not uncommon, after all, many expeditions were launched over the years with the goal of putting a beacon in orbit around an unknown star, so it makes sense that these lost beacons would give off a steady background, but as the Republic knew that the Black Legions were being supplied by a huge shipyard in the Unknown Regions, they were checking every set of coordinates they could find.
Simply destroying the beacon and programming the location of the Star Forge into every ship was also not an option. The coordinates to the Star Forge and the paths leading to and from it were highly classified. Only the very top Dark Jedi had access to them. Any copying of the codes was punishable by death due to the fear that they would fall into Republic hands. As a result, the beacon had to be used, but it was used only at select times.
The Republic did not know what this mysterious source of ships was, in fact, very few of the Black Legion soldiers and even officers knew anything about it either. The whole operation was highly classified due to the danger of its being discovered. Many thought that it was a large shipyard, but a shipyard that large in the Unknown Regions was unheard of. After all, the output of ships and weapons was enough to rival the productive outputs of even Kuat and Anaxes, yet there was no mention of this mysterious shipyard in any reliable star chart.
Most people believed that the Black Legions were in league with a powerful and technologically advanced but small alien territory. This would explain the ship designs and the advanced weaponry that they possessed. Such small and frighteningly advanced nation states while rare were not unheard of. The technological level of the Republic was, in general, higher than most others, but there were some exceptions.
One of the most famous incidents of a small but advanced nation state becoming a threat was the Waymancy Storm. The Storm occurred almost about nine hundred years previously when the Waymancy Hollow, a confederation centered around the planet Waymancy, came into conflict with the Republic. Their soldiers used pulse-wave weapons that were far more advanced than the ones that the Republic used, but even worse were their ships. Their ships possessed turbolasers that were far more powerful and faster than that of comparable Republic weapons, and their shields were much stronger as well. For comparison, these turbolasers were on par with those of the Vong War era Hapan Battle Dragon's while the shields were slightly less powerful than those of a Golan I defense station. Like the Black Legions, they attacked when the Republic was weak, but they did not anticipate that their actions would cause the Republic's massive industrial base to become active, thereby allowing the Republic to match them with sheer numbers until they could reverse-engineer their technology.
Many historians estimate that if the Waymancy Hollow had formed a larger confederation of outer rim worlds thereby allowing them to mass produce their advanced technology, they could have overran the Republic, or at least had been a much larger threat. Much the same had happened in the beginning of the War of Darkness, but now with both sides using comparable technology and a massive industrial imbalance, a Republic victory was imminent.
The Mutiny:
Since the Black Legions had to turn off the hyperspace beacon to the Star Forge for long periods of time, someone had to be left in charge. Usually, a small group of overseers would be left behind to run the station. They were given specific instructions of what to do and not to do, but on the whole it wasn't much due to the fact that the factory was mostly automated. The people put in charge were of many different backgrounds consisting of the most trusted military officers, but, of course, even the most loyal officers can mutiny- especially when their cause appeared to be hopeless and they had to stay in an evil factory all the time.
Perhaps that's the one thing that the Dark Jedi high command underestimated, the seductive power of the dark side, specifically that of the Star Forge. The station was not completely autonomous. It was both a dark side artefact as well as a machine, and so it required a powerful operator or group of supervisors. Those controlling it had to take turns operating the dark side infused machinery as the power had to flow through their bodies. This process, while not exactly painful in the usual sense, had a corrosive effect upon the mental sanity of its victims. Already they were Jedi who had embraced the dark side, and now the machine was amplifying their inner darkness for the sake of the war. With the sorry state of the war and the rebellions breaking out every day, it was only a matter of time until they decided to mutiny as well.
The names of the rebellious Dark Jedi have been lost to history as their data was expunged by the Dark Jedi high command afterwards. They mutinied in the first month of the ninth year of the war. As they were very few living beings present on the Star Forge, it was easy to take control of the station. Historians think that their plan was to form an independent city state in the Unknown Regions separate from both the Black Legions and the Republic, but we can never be sure.
The mutiny was put down quickly. As soon as the overseers failed to signal the beacon at the appropriate time, the high command became suspicious. Pall himself was alerted and he ordered a small group of Dark Jedi to join him to personally investigate the matter. Pall and his followers jumped into the system and immediately flew their ship into the Star Forge master docking bay. The rebels, who thought that nobody would be able to access the Star Forge without the beacon, were taken off guard. The Dark Jedi strike team quickly killed the rebels in the high command room and Pall proceeded to take back control of the station himself. Meanwhile, he sent his followers deep into the factory to hunt down any remaining rebels.
It is unclear exactly what happened next, but given the clues left in Pall's journals, it is possible to piece together a scenario. The official report has been lost and all historians have are indirect testimonies of the other Dark Jedi leaders who were not present. This conflict was the last time that the Dark Jedi were in control of the Star Forge, and we know that Pall wanted the war to end. Pall told them that the rebels had inflicted such damage on the station that the beacon was destroyed, but the other Dark Jedi didn't believe him, or at least they did not believe the whole story. They suspected that something happened there that Pall did not want to come to light. However, the actual explanation is likely a lot simpler. Once in control of the space station, Pall likely ordered the droid soldiers to kill everyone in the Star Forge and to inflict damage upon its internal machinery.
Why would he do this? Pall, and really the rest of the High Command, could see that the war, at this point, was unwinnable, and yet they couldn't just stop due to the momentum of both the Republic and their own forces. Similarly, rebellions were breaking out every day and with the corruptive influence of the Star Forge, keeping it supervised would simply be more trouble than it was worth. Finally, with the advancing Republic line, its discovery would be just a matter of time. Pall did not want the Star Forge to fall into the hands of the Republic, especially not the Jedi, so attempting to destroy it would be the best guarantee.
However, for some reason or another, Pall did not destroy the entire Star Forge. Perhaps the factory's defenses kicked into line and expelled him, or perhaps he had to leave quickly. Whatever happened, when Pall returned, he reported that the Star Forge had been badly damaged and the beacon destroyed. He furthermore wiped the coordinates from any records he could find and forbade anyone to go back and visit the remains.
This, of course, made his leadership all the more unpopular. The war was now entirely unwinnable, yet Pall did not seem to care. He spent most of his time in his study working on huge manuscripts and other writing projects.
In his journal, he writes that he had done everything he was sent to do. In his final years, he came to believe that he was really some type of prophet, sent by the Force for a specific end. Now that he was finished, he writes that the only thing he fears is that an assassin would take his life before he could write down his messages. Sure enough, this was a well founded concern. At this point, he was no longer the acting leader, and yet he was still, technically, the leader of the Black Legions. Many other Dark Jedi were not happy about this and numerous attempts on his life were made, none successful.
At this point, everyone else came to believe that he was simply insane. Despite these assassination attempts, many of the high command didn't mind his presence. After all, he was technically the leader and as such was the object of several plots and attempted coups, and yet, he let his subordinates control the entire movement- or what was left of it. It would simply not be a good long term career move for anyone else to take his place.
The war dragged on for another whole year, then on the first month of the tenth year it all ended at the Battle of Corbos.