The Empire's origins are explained in Episode III, where it replaces the Galactic Republic in the midst of a galactic civil war orchestrated by Palpatine, then the Republic's Supreme Chancellor. Palpatine is also secretly the Sith Lord Darth Sidious who intends to purge the Jedi and restore the Sith to power in the galaxy. Palpatine's Sith identity is only known by a small few throughout his life. Palpatine claims that the Jedi attempted to assassinate him and overthrow the Galactic Senate and declares the Jedi to have committed treason. Palpatine declares that the civil war with the separatists in combination with the Jedi coup d'état require the reorganization of the Republic into a state that can provide stability, and a safe and secure society, a Galactic Empire withhimself as Emperor. The Senate that he has manipulated overwhelmingly applauds Palpatine's decision.

Emperor Palpatine proceeds to purge the Jedi, who had been the upholders of peace and justice in the Old Republic, and replaces them by redeeming the Sith. Though Palpatine's Sith identity remains a secret to most, his apprentice Darth Vader is the Sith Lord who is publicly known to the galaxy as the ally of Palpatine who is serving the Empire to purge the Galaxy of the Jedi. Vader is the ruthless apprentice of Palpatine who is feared by many in the galaxy. By the time of A New Hope, the Empire has transformed into a fully totalitarian regime, with opposition in the form of the Rebel Alliance.

The Galactic Empire is described in various Star Wars