Psienesis wrote:The Galactic Empire is actually much, much older than 20 years. It has always existed as one of several rivals/alternatives to the Galactic Republic (which is, itself, thousands of years old).
Palpatine's Empire lasts 20 years, but that's only following the his coup that unseats the Republic and allows him to take Coruscant basically overnight. The actual seat of the traditional Empire is in the galactic north-east, Ziost, later relocated to Dromund Kaas.
And then there's Korriban, the birthplace of Sith power in the galaxy.
So what Palpatine did was basically, through treachery and guile, achieve victory where scores of Dark Lords of the Sith (Revan included) had failed: he captured Coruscant and toppled the Galactic Republic.
Pretty much all of those empires were, as the various stories go, invariably eradicated. Palpatine, and his line of masters, were wheedling their way in, as they had finally realized after how many failed empires, that the way to control the entire galaxy was to take over the galactic government, from the inside.