The Earth Alliance, headquartered in Geneva, is in charge of the station and the surrounding space.  The corrupt administration of the EA, led by President Clark, has connections to the sinister activities of the Psi Corps, a 
government agency that tracks and trains human telepaths and increasingly seems to be running the government rather than serving it.  An Orwellian agency called Night Watch is stifling any signs of dissent, carting people off to be reeducated if they don't cooperate.  Earth has taken a questionable stance by allying itself with the expansionist Centauri Empire, hoping to save its own skin by allowing the Centauri to roll unhindered over the lesser races Earth once saved.  Babylon 5's commander, Captain Sheridan, along with a small group, is covertly and subtly working to covertly wrestle control away from the current administration, bolstered by evidence that President Clark was directly involved in the assassination of his predecessor.

An old, highly spiritual race, Minbari are humanoid with exterior bone crests on their heads.  Once an adversary of Earth, the Minbari Federation has continued to show interest and friendship with humanity, though how long that 
will remain the case is uncertain.  The balance of power in the Minbari ruling body, the Grey Council, has shifted in favor of the warrior caste, many of whom are none too happy about the surrender to Earth twelve years earlier. 
(Only the Council and a few outsiders know that the war was ended when the Council discovered that some humans carry Minbari souls.) The Minbari have been a major power for well over a millenium, and were instrumental in the defeat of the Shadows, an ancient enemy, when they last rose up a thousand years ago; many are now preparing for another confrontation.

The Centauri Republic, only months ago a fading empire, is currently on an expansionist path.  A deal with unknown forces enabled Ambassador Londo Mollari to regain much of their past glory.  It seems only a matter of time, though, before the deal runs its course and the Centauri find out its price. 
In terms of appearance, Centauri appear human at first glance, though that's deceptive.  Women shave their heads; men wear their hair in fans, with length indicating social standing.  The Centauri Emperor is a puppet, completely under the thumb of several royal houses who have risen to ascendancy with 
Londo's help. 

Once a major power, the Narn Regime has been recently conquered in a brutal assault by the Centauri, especially humiliating since they were unwilling subjects of the Centauri Republic a hundred years ago and had broken free of 
their control.  Former ambassador G'Kar, one of the few who knows that the Centauri aren't working alone, leads a resistance movement from Babylon 5, but his chances of reclaiming his homeworld seem slim.  Narns have a reptilian 
appearance and are easily provoked.  The strict new rules imposed by the Centauri (including the death of the killer's family if any Narn kills any Centauri) have forced them to move carefully.