Okay, lotta people look at the Thrawn Campaign and say, "Where was Palps? Why didn't he help? Why did he even help the campaign fail according to some? Why did he allow the Imperial Mutiny?"
Many chalk these things up to Craziness, megalomania, Social Darwinism etc(And to a degree they are.) However there are some very logical(Though in hindsight self destructivly fatal) reasons Palpatine did what he did during both.
First off with Thrawn. Thrawn returned and reunited the rim factions into a confederation with himself at the head to save the Empire. During this time let us look at Thrawn's actions and how Palps would have interpereted them.
Thrawn returns, reunites the factions but makes no contact with Byss(Possible he didn't know palps was alive, but suspicious to Palps point of view). He immediately begins rallying and personally becoming an icon of the Empire(Which Palps had been very careful to avoid Thrawn doing until now) He procures HUGE amounts of Ysalamiri gains cloaking tech and clone facility to build and army loyal to HIM. Thrawn tells many that HE is the ruler of the Empire now, not some long dead Emperor(Thus stating his independance publicaly) Finally he gets a mad VERY powerful Dark Jedi and plans to clone him as a future Emperor(Now we have moved into what looks VERY much like Thrawn countering every advantage the Emperor would have had, thus making him VERY dangerous to the Emperor)
Thrawn was loyal to the ideal of the Empire, and his OWN version of that ideal differed from Palps vision, so why would he submit when he now held the power?
So of course Palps would not want Thrawn to succeed if it meant he would be supplanted by him.
Now for the Imperial mutiny. Why didn't Palps just come out and say, "Here I am! I am the Emperor, listen to me again!"? Simple. Each Warlord was independant, yes they were VERY loosely allied to take Coruscant(Most likely because each thought that they could benefit from it and then take power) During the Emperor's reign he always had a leash on these Admirals, Moffs and Generals via the Stormtrooper Corps, the ISB and the Inquisitorious. Now, that leash no longer existed. Most Stormtroopers were recruits or Army troopers loyal to their Warlord or sector. The Inquisitorous was largely destroyed and the ISB was a pale shadow of it's former self.
As a result all these commanders now held vast amounts of Military power in their hands, not Palpatine's. What was to stop them from refusing his orders? Or outright trying to kill him? Nothing but Palps own forces, which while powerful were not equal to the Entirety of the combined Warlord Fleets. Also while they were called the IMPERIAL Warlords they were each seperate nation states that were exceptionally hostile to any outside control. These were not Allies, they were ALL enemies as much as the NR to any power other than their own. His solution? Have them destroy one another and then step in as the dominant power when they are weakened. It's easier to fight one enemy than dozens. So he funnelled their hatred of each other so they would fall into internecine conflict. The result, they were devastated, badly mauled and weakened and to boot they had chased the NR away from the Core. Then Palps made his appearance in full force. With his superweapons, centralized stability and the rewards he gave the survivors of the Mutiny they submitted to him. His plan worked very well. He was back in charge, his enemies had torn themselves apart and with his clones, essence transfer, and the superweapons Palps had no doubt he could destroy the rebels who had been pushed to the corners of the galaxy anyway. This can be largely attributed to his ego, having cheated death and his enemies being so scattered and weak in comparison to him now. All things considered Palps plan was very efficient and well conceved for destroying Rival Factions....the problem was that everything hinged on HIM surviving as the center of the Dark Empire...without him it went back to factions...factions that were badly weakened and badly bitter toward one another for what each saw as the others fault for their own weakened state. With this divided and badly weakened Empire spread out over virtually the entire Galaxy it was relatively easy to reconquer especially as fed up as most of the Galaxy was with the madness that passed for Imperial Warlords and what insanity had been the Dark Empire. Add to this no legitamate Heir to the Throne, internecine thoughts and dwindling resource pools the Empire was dealt a death blow as a direct result of Palpatine's schemes.