In the brikwars multiverse, all battles just happen. Every user has an area of space, but judging from the battle organization forum, none of these civilizations ever meet. Except by using time and light travel (forum battles)
But we really don't need this. The only reason Magic Soap(me), NatalyaAF, Roc77, Strana and Tuefish are on the map are we have heavily themed armies which all fit in with the background of Galaxia Nehellenium. But on a bigger scale, Galaxia Nehellenium is but a small dot.
But if 501stCadians, you want to get some other users and make your own brikgalaxy, there is nothing stopping you.