It was very strongly hinted at in various EU books around the time of the NJO, particularly Rogue Planet. Palpatine chose that moment in history to take over the universe because he thought the Jedi would lead to the downfall of the entire galaxy. He later sent Thrawn out that way, because he saw the Vong as a bigger threat than the Jedi, who he could wipe out with a bunch of New Zealanders in colorful white armor. Palpy never comes out and says, "Hmmm, I think I will take over the galaxy now because these aliens from another galaxy are bad news," but it's definitely intended to be the case.
It really got into it in Outbound Flight. While it was a good book, the whole good guy Palpatine thing was over the top.
Originally Posted by bigbarada
I remember that alien-bigotry explanation and I definitely never felt it to be satisfactory. As for Palpatine trying to prepare the galaxy for the Vong invasion, that's sounds like the plotline for Fable III, but the Star Wars version probably came first. Either way, trying to attach some sort of "noble" motive to Palpatine's actions completely undermines the storyline for all the movies. That's a horrible idea.
The Thrawn trilogy said it was alien bigotry, however later books said he kept his top tactician out there to be on the look out for Vong forces.
Nowhere in your incoherent ramblings did you come anywhere close to the answer. Thanks to you, everyone in this room is now stupider having heard you. I award you no points and may God have mercy on your soul. -Billy Madison-