As if the stakes weren't high enough in The Rise of Skywalker, Palpatine was revealed to have assembled the largest fleet of Star Destroyers in history as part of his elaborate Final Order. This was certainly an excellent expression of force and might, but it left a lot of questions unanswered.
How exactly could Palps assemble that large of a war effort in the 30 or so years since he was thrown to his death? Did he have help? Was there time dilation? Now, a new theory uses an old Sith factory from deep in Star Wars history to explain it.
Reddit user Luy22 suggest the Sith Citadel, the looming castle on Exegol where Palpatine was apparently hiding all this time, is actually a Star Forge, the ancient Sith automated shipyard created 30,000 years before the events of the original trilogy in the non-canonical Star Wars Extended Universe. Known best for its appearance in the video game Knights of the Old Republic, the Star Forge could manufacture thousands upon thousands of battle droids and reinforcements for the Sith in the Jedi Civil War.
The most interesting aspect of the Star Forge is the way it drew its power. Stationed nearby a star in the Rakata system, the Forge could suck up the gases and energy and use that to fuel its manufacturing process.
The biggest piece of evidence against Palpatine building a Star Forge of its own is the star power. Exegol is a very dark planet, and the Citadel is firmly planted on its surface. How could it possibly generate its own power? Perhaps there's a simple canonical answer like a fiery planet core the Citadel is able to capture or a dark star in a nearby system combined with some Star Forge 2.0 technological advancements.
Whether or not Palpatine is space fracking, a Star Forge would be one of the best answers to how he was able to assemble such a large army in such a short amount of time. Still, it begs yet another question: how could Palpatine learn of such ancient technology? Was Darth Plagueis in possession of the secrets to the Star Forge as well as the secrets of cloning?
The Star Forge was destroyed at the end of the Jedi Civil War, millennia before Palpatine was even born. So the possibility of him somehow learning the tips and tricks to automated manufacturing and seemingly infinite energy seems rare, but be careful not to underestimate Sheev Palpatine.
That's how he ended up with a giant fleet in the first place.