Theory of the fading suns:
Because suns have only a limited lifespan, those cool out the fastest being the farest away from galactic core. Of course new suns are born from time to time, but even sun-birthing gas clouds are exhausted at some point.
So the general idea is the suns die from outside in according to entropic rules.
Space-traveller civilizations (and they have to become space-travellers or perish - living without a sun is not possible, except for hydrothermal vent communities feeding on tectonic energy) have to wander from outside in twoards the galactic core. Its leading to a gigantic galactic exodus coreward affecting the entire galaxy.
My guess is the coreward front of the exodus wave reached Vasari space and they got steamrolled by a neverending wave of hostile civilizations fighting for survival, eagerly working their way twoards the best worlds in the galactic core of their sector of the galaxy.
The Vasari moved themselves farther coreward, fleeing from the menace and now form themselves the spearhead of the exodus coreward front, as all the others do wich follow them.
It ultimately will lead to a gigantic war at the galactic core, fought by the most powerful space-travellers bend around the control of the last dying suns in the far future. Until even those perish.
The most beautiful aspect of this idea is there is always room for a new civilization joining the fight because the exodus wave throws everything there is in the sector sooner or later.