Father Skywalker said:

Darth Vader/Anakin Skywalker, did want to be the ruler of the galaxy himself. Being a Sith Lord, the evil sith have a habit/tradition of overthrowing and killing their sith masters and taking their place, like a power struggle amongst each other. The sith are like a real group of backstabbers.

Instantly stuck in my head.

I always like to see it as the Empire being good and holding the galaxy together, like the Republic did, and the Rebels being evil terrorists intent on disrupting the legitimate rule of the Empire in order to throw the galaxy into chaos and anarchy.