"Major wars between interstellar civilizations are really quite rare, most of the time they aren't seen as worth it for either side. When they do happen I think it's almost never to the death? And even when it is, I think it's unlikely to result in all sides getting wiped out, usually at least one side is left in a position to rebuild relatively fast. Most of the time it ends in some form of peace well be-fore that point."
"Wars between mega-civilizations involving hundreds of planets on either side might be more common, but mega-civilizations are too new to be sure - we only know of three extant ones: the Federation, the Amalien Alliance, and the Borg. I think we have evidence that at least one other one existed in the past but we don't know much about them or where they went."