An ambitious, ruthless proponent of military power, Wilhuff Tarkin became a favorite of Supreme Chancellor Palpatine and rose rapidly through the Imperial ranks. Shortly after the Empire's creation, he was put in charge of the construction of the Death Star. Tarkin saw the Death Star as a way to crush all dissent to the Empire's rule -- fear of the station's planet-killing superlaser would keep the galaxy's star systems in line. He demonstrated the station's power by destroying Alderaan, but died soon afterwards when the Death Star itself was destroyed.
The Citadel was intended as a flawless contingency for an unthinkable problem -- the stark prison was built to hold Jedi, should any in the Order ever turn against the Republic. Constructed 500 years before the Clone Wars, it fell to Separatist control when the planet Lola Sayu was conquered by the Confederacy early in that conflict. The Separatists populated the prison with battle droids, and used it to hold Republic captives. It is an imposing, heavily armed fortress seated atop a monolithic butte.
For over a thousand years, the Galactic Republic stood firm as a democratic union that governed the galaxy. The Republic was governed by the Galactic Senate, consisting of elected officials from each system and world, and Jedi Knights served as peacekeepers. With the rise of Supreme Chancellor Palpatine, however, the Galactic Republic -- and democracy -- would crumble.