Their race better have a VERY long lifespan then. Why build an interstellar "empire" if you can't live long enough to enjoy it or even administer it? A race could colonize other systems, but since communications and travel are limited by the speed of light at best, political organization of an interstellar "empire" would be very hard or outright impossible. Basically, each system would be its own independent political entity and cultural "petri dish" evolving independently from fellow members of their species in other systems.
Perhaps therin lies the best hope for freedom there is. Just pick up and move to where nobody else is willing to follow you. I don't know how easy it'd be to do so, since there's a lot of variables (access to transport, willingness to leave the homeworld, availability of habitable planets, terraforming, etc.).
Hell, mabye every culture eventually evolves Democrats to muck things up?
I agree -- you either solve the problem of faster than light travel OR increase life span to virtual immortality to make a galactic empire feasible.
One wouldn't have much of an empire, true, absent some faster-than-light technology, or magic, or something. A civilization might realize, however, that it is likely not alone in the galaxy. It might understand, too, that all it would take is one other civilization to start colonizing the galaxy for the whole place to be occupied. Rather than risk getting overrun by aliens, this civilization might figure it's better for it to start colonizing. And there we are.
Then there would be the "99.99% travelers" moving near the speed of light would slow their time down to 1/70 of "flat time" A worker over ten years would oversee 700 years of "flat" time.
Then some would live at 99.999999% of the speed of light and the time dilation would be more like 1/700 or some such. They could regulate over thousands of years.
Here's another thought. If someone takes a trip 10 light years away and is going so fast that time is slowed down by a factor of 10, doesn't it seem like to them that they took a 10 light-year trip in only a year? Doesn't it make it seem like to them , that they are traveling 10 times the speed of light?