system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] What would have happened If the Emperor informed the rebellion about the future invasion of the Yuuzhan Vong and the true purpose of the Death Star(granted they could convince the rebellion that was the case)?
gpt
Neither the Death Star nor the Empire itself was created to fight the Yuuzhan Vong. 

The Sith had been planning to kill all the Jedi and take over the galaxy since forever. It just so happens that if you're about to pull that stunt off, and you get a tip about a powerful extragalactic force planning to invade, then yes, you try to prepare for that. Good thing you were planning on consolidating all martial might in the galaxy under your command anyways. But anyone who says that Lord Sidious was simply trying to save the galaxy is a nothing more than a particularly dense conspiracy theorist.

****

The question is still good, though. What if the Emperor told the Alliance about the Vong, and they were totally convinced of the threat? What would people do differently?

**The Stupid people in the Alliance** (e.g. Bothans)

The Alliance has it's share of politics-playing douchebags who would see the galaxy burn before admitting that someone else had a good idea. The Bothans in particular have a proven history of putting their own desire for influence (even merely *perceived* influence), ahead of any strategic or moral objectives. They will eagerly deny any truths they can just for the opportunity to belittle someone who wants to do something about it. 

This part of the Alliance would deny and downplay the Vong threat, and even sabotage any attempts to fight it. Indeed, when the invasion did occur in the New Republic days, these petty politicians did exactly that. In this case, they would accuse any Rebels sympathetic to the the Empire's desire to fight the Vong as traitors, and try to eject them from power. They would argue that The Vong are an Imperial fabrication, that their Alliance shouldn't resort to violence against the Vong, and/or that anyone willing to cooperate with the Empire was just showing their true traitorous colors. 

**The Open-minded people in the Alliance**

They would still oppose the Empire for it's unnecessary genocidal and racist actions, which they could rightly argue weakened the galaxy. Even if they bought into the idea that the Emperor was doing it all for the greater good, as morally individuals and representatives of their people, they would still insist on participation in the process of preparing for it, and on exploring all options for dealing with the Vong. They would find themselves unable to work with the Empire on this. 

Some of them would feel it was *more* important to overthrow the Empire, though perhaps in a different manner. One more focused on the supplanting the politics rather than sabotaging the Empire's direct physical might in the galaxy. 

Others might decide that the rebellion would have to wait, and do their best to prepare the galaxy in ways that would piss of the Empire as little as possible. Head to the outer rim, where the Empire doesn't have as strong a presence, and try to build up a strong resistance, possibly with the help of crime lords with enough influence to keep the Empire off their backs.

**The Empire**

Sidious and his Empire would still not tolerate Senators trying to make decisions, or non-humans having any say at all, or anyone denying his absolute authority in all things. Tarkin would have still blown up Alderaan, just to convince the naysayers that the Empire is the one the in charge, no questions asked. 

**TL;DR Best case scenario:** The Rebels still fight the Empire, not much changes.

**TL;DR Worst Case Scenario:** The Rebellion fractures due to infighting after their common enemy no longer is so. It doesn't reform until after the Vong threat is dealt with in some way, but by then people are more eager for stability than they are freedom.