There's way too much anti-Imperial bias in here. I think the circumstantial evidence that the Empire was preparing for the Vong is overwhelming.

For one thing, why build the Death Stars? The resources used for a single Death Star could build dozens of Star Destroyers, and area bombardment by a fleet (e.g. Taris) can destroy a planet almost as easily as the Death Star's superlaser. The Death Stars don't do anything more to advance the Tarkin doctrine than a new fleet would, so why are they built and especially why is a second one built after the first revealed weaknesses a SD fleet wouldn't have had?

Because the Death Stars are designed to destroy YV worldships. That's the only advantage over a conventional fleet, but it would have been huge in defending against the YV invasion. If the Galactic Empire has maintained its dominance and had multiple Death Stars at the time of Vong invasion they would have saved trillions of lives.

There is no direct evidence for this theory. There is circumstantial evidence, as /u/McGravin points out, but it is extremely speculative. What we know about Palpatine's personal history is that he was extremely ambitious, and sought power at the expense of order, liberty, and equality. Seeking an objective view of Palpatine's empire is good, but sometimes objectivity leads us to the same conclusion as that for many dictators on many worlds: sometimes people are just bad.

The counterfactual speculation as to what the Empire would have done about the YV invasion is an interesting one, and the strong, determined fight by the weakened Imperial Remnant when the Vong invaded in 28 ABY lends some evidence to the idea that a more unified and militaristic government might have staved off the devastation wrought galaxy-wide by the invasion, but it remains speculation.

The fact that Palpatine sent a task force to destroy the Outbound Flight expedition might be support for this theory. It's possible that Palpatine was already aware of the Yuuzhan-Vong at the time and did not want the expedition to come into contact with them before the Republic/Empire was ready to deal with the threat.

The idea that Palpatine expanded the Imperial Fleet is actually a common misconception. You have to remember that the beginning of his reign coincided with the end of the Clone Wars, which saw the Empire inherit tens of thousands of vessels from both the Old Republic and the CIS. In the years leading up to the Civil War, the Empire actually decommissioned almost all of these.

At the same time, the Navy went through a process of rapid modernisation that saw many new and powerful classes of ships built, such as the Star Destroyer, that outmatched anything that came before it. This is where the misconception comes from. While thousands of these were built, the size of the Imperial Navy was still a fraction of the force they inherited.

If Palpatine was truly aware of an imminent threat such as the Yuuzhan Vong, he would have kept the fleet at wartime levels.

I think it's beyond argument that had the Empire remained in power during the invasion, significantly less than 365 trillion beings would've been lost. The rebel Republic's risible habit of treating plainly hostile civilizations with "diplomacy," paid bloody dividends. I sometimes wonder if the rebels realize what they brought on by deposing the rightful leader of the galaxy.

This proposal always seems to me a blatant piece of Imperial apologia, often clung to by people too willing to believe Imperial propaganda. I believe it has its roots in the tendency of some authors to attempt to fit every strand of history together into a cohesive and linked hole. History does not work like that.

For me there's a simple counterargument to this. If Palpatine was indeed worried about the Yuuzhan Vong invasion, why did he never tell anyone else? No Imperial official ever shows any foreknowledge of the Vong. Why does the idea of an extragalactic threat appear in any known propaganda, pre- or post-Palpatine, despite the fact this is ideal propaganda material?

This argument extends to Grand Admiral Thrawn, one of the Empire's greatest military strategists, and involved in the destruction of the Outbound Flight Project. If he was aware of the Vong, Thrawn failed to pass on this key information to his second-in-command Pellaeon, who was as unaware as anyone of the threat.

There's potential confusion here between the idea that Palpatine was preparing to defend against a possible threat from outside the galaxy and that he knew about the Yuuzhan Vong threat. Palpatine is well known for his paranoia and determination to maintain power. It's plausible that he might have been considered an extra-galactic invader a possibility and even have acted on this concern. This does not mean he had any specific foreknowledge.

This is a common argument used by Imperial revisionists to justify the Tarkin Doctorine. While this is a seductive explanation it fails to account for the fact that focus of the imperial build up for the first 20 years of the Palpatine administration was the first Death Star. While the Death Star was a tool of power never before seen in this sector of the universe its superlaser was only accurate enough to hit planets, not Starcruisers. Such a weapon would have been useless against the Yuuzhan-Vong but not against rebels striking from a hidden base

I'll tell you one thing: there's no merit to the much-bandied conspiracy theory that the Empire rediscovered the ancient Rakatan super-factory called "The Star Forge," and used it to power the war effort.

Accounts of Revan's life, "death," and disappearance vary, with some saying he destroyed the Star Forge and disappeared from history, and others claiming he took control of it, but fled to the far reaches of the galaxy. No matter which version you accept -- and there's much more evidence, based on apocryphal accounts of the the Ebon Hawk's navigation logs at least, that he destroyed the Forge -- nothing in the historical record suggests the Imperial buildup was attributable to the Forge. Indeed, what we know about Imperial production capabilities, such as its reliance on Seinar Fleet Systems, rebuts the notion that it ever controlled a mythical Force-powered superfactory.

Absolutely. The creation of super weapons is direct indication of the preparation for the invasion by the Yuuzhan Vong. Take as evidence the Death Star which was meant to destroy world sized objects, including but not limited to to World Ships that were transporting entire domains of the Yuuzhan Vong. Now, of course, being the pragmatist he was, Palpatine also intended to use these weapons exactly how he did, to suppress rebellion against his rule. But especially the Death Star project and the Galaxy Gun indicate to a confrontation with his known foes. Palpatine had known about this threat from his encounters with Thrawn, Outbound Flight, and the infiltration of Nom Anor later on around the events of the uprising of Carnor Jax.

But I think here is where a line on the supposed "goodness" can be stopped at. Palpatine desired power simply, and I believe it was his intention to rule his empire regardless of who threatened his power. He builds these weapons in anticipation of the invasion by the Yuuzhan Vong, but believes them to be no different than the rebel alliance. Palpatine surely did not come to power to save the galaxy if that's the larger question you're asking.

Neo-Marxist historians of the New Order Period have argued that the Imperial Navy was a make work program designed to drive down galactic unemployment at a time when droids and slave labor had made workers superfluous.

It seems unlikely, as even Palpatine knew about the Yuuzhan Vong, his more immediate goal was to establish and consolidate power on himself. From the deceleration of the Empire to the destruction of one of Yavin's moons, Palpatine grew the military to act as warlords so he could dissolve the Imperial Senate which he did in 1 BBY. The Moff's and Grand Moff's would act as Imperial bureaucracy. To accompany this, after the devastation of the Clone Wars, the empire embarked on large scale naval building programs, (and other standard shows of force for autocratic regimes) to show off the power of state and bolster confidence in this new government. This is all the common history and well known.

There is recent scholarship documenting a certain grand admiral, and his campaign to reestablish Empire control in the waning days of the Empire, talks about the system of Grand Admirals put in place by the Emperor. The work of Zhan et al posits that Palpatine picked the Grand Admirals such that some of the greatest military talent would be under his direct supervision and micromanagement. Well known is Palpatine abilities in persuasion, such so that many consider it to be otherworldly, so controlling a small number of brilliant military commanders allows him to control a slightly larger number of Moffs whom control his empire on a day to day basis. In order for this to occur a large military was very much necessary.

The central tenet to this argument is that Emperor Palpatine did in fact have knowledge of the Yuuzhan Vong prior to his establishment of the New Order, which he did in fact have due in part to his incredible ability to foresee the future.

As u/c1ae mentioned, Palpatine, upon ascending to power as the Galactic Emperor did in fact cut back on some of the ships in the Republic (now Imperial) fleet from wartime size and instead overhauled the fleet with standardized ships and the latest weaponry. However, this is assuming Palpatine began preparing for the Yuuzhan Vong when he became Emperor, however I believe this is a naive approach to the Dark Lord of the Sith's strategy.

Palpatine and Plagueis had been planning their takeover of the Republic and the establishment of the New Order for decades before it finally happened. Indeed, the Separatist movement and the Clone Wars were orchestrated by Palpatine in order to have a sudden rampant increase in the amount of available military technology and equipment in the galaxy while simultaneously readjusting millions of planets to wartime production which had not been seen in almost one thousand years.

Also, we must also take into consideration the fact that Palpatine likely did not know exactly when the Yuuzhan Vong would arrive. Indeed once the Clone Wars began, if the Yuuzhan Vong arrived Palpatine would be able to make a short-term alliance with the CIS in order to combine their vast military strength against the Vong in addition to the fact that the Vong would be a chance for Palpatine to send thousands of Jedi to their deaths against the fierce Vong warriors and also allowing Palpatine to further centralize his authority in preparation for the New Order.

Further evidence of this is seen in that the Separatists, who were under direct control of Count Dooku, who in turn obeyed Palpatine, constantly spent Separatist resources constructing new superweapons only to have them repeatedly destroyed by Obi-Wan Kenobi and Anakin Skywalker, much to the chagrin of Sidious and Tyranus. Add in to this the fact that in one instance the Separatist had literally constructed a weapon that destroyed biological, but not synthetic, material. This is exactly the kind of weapon that would have devastated the Yuuzhan Vong and their biological technology.

These arguments, combined with those made by others about the various actions Palpatine undertook once he had ascended to Emperor validates the fact that Palpatine's true endgame was preparing the galaxy for war with the Yuuzhan Vong.

According to the revised history of the galaxy, the Yuuzhan-Vong never existed. Did you not get the memo?

There is plenty evidence that the Empire learned of the incoming invasion beforehand, but the autocratic culture of the Empire goes far beyond that, finding its roots in the Republic Armies support of the Declaration of a New Order. The Empire obviously only learned of the invasion after its foundation. Why would you destroy such a useful force such as the Jedi Order when you faced such an advanced threat?

Truly the Empire was not founded to fight this threat or else the Human-centric policies would not be in effect to create a more cohesive fighting force. How could you fend of extra-galactic invaders if your army is purely humans and increasingly impure clones?

The New Republic Response was poor and in fact caused the collapse of the Republic and the formation of the Galactic Alliance. The Imperial Remnant was sabotaged by the Yuuzhan Vong to cause even more fracturing.

To truly understand the Invasion you have to look at it at a wider scale. It was in reality a trans-galactic mass migration, and the war merely a reaction to this dynamics change. Old species were pushed aside, planets moved, and the post-war galaxy was forever changed with a new, massive species living in Coruscant and around the galaxy.

This isn't even canon anymore :(