The planet Bajor has liberated themselves from the oppressive reign of the tyrannical Cardassian Union and to aid in the reconstruction efforts, Starfleet has taken control of the Cardassian's abandoned space mining platform.
But the discovery of a stable wormhole that provides instantaneous transport to the unexplored Gamma Quadrant 70,000 light years away and inaccessible by normal means makes Bajor a new major center of exploration and trade. This attracts the attention of the Cardassians and other hostile powers once more.
And so this dilapidated space station is reborn as the main hub for Starfleet and Bajor's defensive, political, and economic interests. A home away from home for pioneers and explorers, traders and soldiers; it is called Deep Space Nine.
There is a long standing controversy regarding claims that DS9 was heavily influenced and based upon J. Michael Straczynski TV series,Babylon 5. Reputedly, Straczynski pitched the series concept and a extensive bible of story notes to Paramount Television well over a year before DS9 was released. Although Paramount turned down his project, the timing of the launch of DS9 and its similarities have led to his belief that the studio heavily utilized his notes as the basis of DS9.