The Galaxy RE-524 is a galaxy inhabited by 2 massive factions, who are currently at war, utilizing the technology of extinct races: the Imperium of Reclamation, which uses Forerunner Technology and was founded by a human who was composed by the Forerunner Composer device but was made fully independent; and the Dominion of Air and Darkness, who utilize Iconian Technology and was founded by a human who was turned into an energy being using Iconian Technology.
Multiple other, smaller factions are located in this galaxy, but they have to concentrate on avoiding the warring super-factions.