Here's how it is,
The earth got used up. So we moved out, found a whole new galaxy of earths to call home. Some rich and filled with the new technologies. Others, not so much. The central planets, those form the Union, who raged war to bring everyone under their rule. Few idiots tired to fight it. Among them, myself.
I'm Kenna Reynolds, caption of Serenity. She's a transport ship, firefly class. Got a good crew. Fighters, pilot, mechanic. Even picked up a missionary for some reason. And we have a glorified companion on board. There's a doctor to, took his screwed up sister out of some union camp so their keeping a low profile.
We live by a code, it's pretty simple. Find some work, stick to your own, keep on flying.
You got a job? We can do it. Don't much care what it is.