Rebel Alliance.
As attractive as the idea is to "bring order to the galaxy," the Empire went about it all wrong. Do we get caught up in the technological "coolness" and forget that the Imperials denied equal rights to non-huMans, enslaved worlds, sought to bring order through fear of destruction, and tortured/killed all those who opposed them.
Palpatine and Vader were evil men, who did evil things and brought dark, oppressive times to the galaxy. Those who stood up against it did the right thing.
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Ah, dang, Isuwen beat me to the punch.
JediKirby: The books show the tyranny of the Empire better than the films; ones that come to mind are the original Star Wars novel, the Farlander Papers (X-Wing strategy guide), Star Wars: Empire: Wrong Side of the War comics, and the Allegiance novel that just came out.