The recent past, of course, was the Battle of Yavin 4- in which the Death Star was destroyed by Rebel forces only seconds before it would have blasted the moon into oblivion. In that time, the moon had served as the base for the Rebel Alliance, led by Leia Organa. The Rebel Alliance; a brotherhood of rogues, scoundrels and outcasts which had evolved into the New Republic of today. Into an unmatched military and political force in the galaxy.
The far flung past was that of Sith and Massassi, darkness and hatred, the Dark Side. The Massassi had been a mutilated race of warriors and murderers. When they were found by a cunning Sith Lord, they were warped even further, into dark and evil beings living to serve the sick will of the Dark Side.
Spirits of dead warriors and Sith still haunted the moon, causing havoc whenever it was possible for them to do so.
Which called into question the choice of Gash Jiren to place his Rogue Jedi Praxeum on the planet, and even more so the choice of Luke Skywalker to place the first Jedi Academy on the troubled forest moon, in his days of rebuilding the Jedi Order. Gash had done so in order to inspire students with the planet's Rebel and Jedi past, to spur them on to greatness with the memories of warriors and heroes long past. That, in addition to the Jedi Master's belief that knowledge of- not sheltering from, as some Jedi suggested- darkness was the best tool for combatting it. Better that one of his students be tempted by the Dark Side while they were still Padawans, and under his watchful eye, then as fully-trained Jedi Knights experimenting with darkness outside of his supervision.
Luke Skywalker, on the other hand, was simply a fool.
Not mentioning the other Jedi Master's staunch opposition of Gash's ideals at the recent Jedi Council meeting, Luke's placing of the Jedi Academy on Yavin 4 without warning or foreknowledge reinforced Gash's opinion of him as a Jedi with nothing but luck on his side, a man who acted without thought or intelligence.
But despite the planet's usefulness as a training center for young Jedi, Gash had already decided it was completely useless as the capital of a faction, nation or empire. And certainly, it already appeared that the Rogue Jedi Order was seeking to become just that. The new faction's prompt acquisition of Gash's homeworld, Asthentia, made that apparent.
In truth, Gash had not intended they take the planet, nor had he known there was any chance of that happening when he set off to defend the planet from the pirate assault. But that eve, a vision had come to the Jedi Master... a vision of the Rogue Jedi Order as just that, an order; a united force ready to confront and deflect the evil to come in the times to come.
So Gash now searched his datafiles for a suitable world to place the capital of this new Order. A few hundred words passed across his screen... then...
Ossus.
The former capital of the Jedi Order itself in the days of the Old Republic. Yes, Gash had heard of the magnificient city world, now ruined by decades of fighting. All that was left was ruins, rubble, wreckage... scattered tribes, factional fighting. A few descendants of Jedi.
Perfect. A way to not only improve the way of life on a planet, and further the cause of the Rogue Jedi Order....
Gash tapped the communications console on his desk, smiling and nodding briefly to the image of D31, his not very droid-like droid aide, which promptly appeared.
"DeeThree... mobilize the Hermes and all of our fighters. I'll be down in an hour."
'Right. Where are we off to this time?'
"Ossus."
'The Ruined World? Why the hell-'
"You'll see, you'll see."
'Whatever, Jiren. You better have a plan.'
In fact, Gash realized he stood and walked to the door of his office, he didn't. But a little recon on the ravaged capital of the Jedi Order sounded a good place to start.