Stability and not-expanding are not necessarily the same thing. ("Stable" is easier to write.) They could be extremely dynamic, but if their population isn't ex

Stability and not-expanding are not necessarily the same thing. ("Stable" is easier to write.) They could be extremely dynamic, but if their population isn't exceeding their resources, why do they need more room? Expansion is what brings cultures into contact and conflict. Puny humans are confined to one solar system, and even just the one planet, but are pretty dynamic. Population in wealthy countries is in decline. Remember we are not just talking about humans with bumpy heads, here. Social universals on Earth do not apply. Expansion might be limited just by a physical inability to reproduce beyond their home planet, without giving up any dynamism.