Hegemonic Empire: The Empire, absolutely. Since the old days of the Consolidation Wars back on the homeworld, the consensus culture of the Empire (individual exceptions like the Imperium Bellipotent and a few grumpy occasional reanimators of the Doctrine of the Ecumenical Throne notwithstanding) is pretty sure that military imperialism has some awkward conflicts with their core values, and in any case is pretty much a pessimal way to grow.

The new plan is to seduce the universe – or “corrupt” the universe, if you are prefer to phrase it the way the Voniensa Republic, the Socionovist Association, and the Interstellar League of Tribal Chiefdoms do – and make everyone want to be part of it via Rule of Cool, manifested in such newfangled soft-power traditions as building and operating major infrastructure, being economically ubiquitous (thank you, All Good Things, ICC), potent cultural perfusion selling the Imperial Dream and other such notions (thank you, media studios of Delphys!), peddling immortality and personal enhancement to anyone who’ll buy them, etc., etc. And the good thing about this, say the people running the place, is that the only actual policies they need to have are (a) open immigration, and (b) mostly-open admission to any polity that asks for it – which by that time have almost certainly been quite “Imperialized” anyway. The rest is more or less self-driving, and would indeed be hard to stop even if they suddenly became of a mind to.

The success of this strategy is such that, discounting colonization of entirely unoccupied worlds and regions, virtually the entire growth of the Empire in its interstellar period has been via voluntary admissions – and it maintains quite the sprawling sphere of influence outside that.