Well the Vitrus empire has always existed just more so in our heads and not terribly fleshed out. The idea being that the war gave some power to more minor factions within Human space to rise up and sieze power. One faction being the Order of the Mother Bear (Space USSR basically) and the Vitrus Empire (Space Romans). They are smaller factions than the human Earth based government but still own quite a few planets. The Sovereignty is close trading partners with the Vitrus in an attempt to undermine the human government basically but they hate the Order of the bear. Them hating the bear since they essentially use the big bad aliens as a way to stay in power and keep harassing fringe worlds, so when they become bothersome enough the Sovereignty goes in and does some house cleaning with Bear bases of power. Their allowed to do this since they are not part of the assembly and the mainline human government hates both groups anyways.