welcome to the 'verse
Earth-that-was became barren and uninhabitable, so humanity packed up its bags and made outer space its new frontier. Terraforming converted planets into colonies of varying status, some rich with technology and others poor and primitive. The core colonies became the Alliance, and the Alliance became a force to be reckoned with, seeking to take all of the other planets until their power. Then came the Unification War. To sum it up, the Alliance won, and the Independents? They lost the battle, but they weren't completely defeated. Many of the surviving Browncoats scattered to the edges of the 'verse, doing what it took to survive under the new regime.
That was seven years ago. The year is 2517 A.D. This is the story of the crew of a Firefly-class starship that's doing just that -- doing what it takes to make a living in the outer planets, whether it's legal or not. A job's a job, right?