in b5 the centuari and narn hate each other and have been having minor conflicts for a long while, in season 2 it turns into a full scale war and the centuari use mass drivers on the narn homeworld. prior to that the narn were equally or maybe even more bad than the centuari in terms of representation to the audience, they are viewed more sympathetically and the crew helps their underground movement but they do it clandestinely because earth-gov and the centuari have an alliance. even with that help operations against the centuari are not exactly encouraged. b5 is united nations in space, with the humans, narn, minbari, centuari, and vorlons as the security council, they all had heavy influence on the station but its human operated and the vorlons almost never do anything and the minbari are generally honorable, almost insanely so, the centuari and narn do most of the intrigue stuff and have influence everywhere, at least until the centuari conquer narn which clearly hasn't happened yet in game.