It started as a joint US/Russian project, but as relations between the two countries fell apart, the Russians pulled out and went back to their own space program. The station was intended to be a waypoint for explorations to Mars, but work on it went very slowly until the invention of the mat-trans, at which point it became much easier to transport materials.
When World War III hit, the station was attacked by several Russian satellites, which damaged large parts of it. The inhabitants who weren't killed fled the station, using the gateway to jump to parts unknown. The station itself is still (mostly) habitable and has power, but very few know of its existence. (Homeward Bound, Parallax Red)