A faction in the WWR Universe is a term used to describe the different forces involved in the Great War. Known main factions are the Terrans, Martians, N.O.M. and M.O.D.. There are other sub-factions or auxiliary groups involved in the war such as MERC, the Lunar Defense, and the rogue Nom de Plume.
The term faction is specifically different than "nations," which would have allegiance to the faction of their choosing.