A European Empire covering the entire White world would have the benefits of preventing intra-European conflict caused by competing state interests. There is no doubt that, historically, such interests have typically overridden professed common Christian or European interests. Such an Empire would also have advantages of scale not available to the medium-sized nation-states of Europe or even of the 150 million or so souls of Russia or of a putative White Republic of North America.
Such an Empire however would have the disadvantage of intra-European ethnic and linguistic diversity, leading to the usual conflicts, inequalities, loss of cohesion, fractured consciousness, and so on, that one finds in multicultural regimes in general (and in the still majority-White EU/Eurozone, Belgium, or Canada). The nation-state, in contrast, is internally more optimal, having but one language, one consciousness, and one cohesive polity and society, as opposed to an inevitably messy federal and continental regime.
Personally, while I see obvious benefits in a limited union of the nation-states of Western and Central Europe, I am wary of a single “mono-state” for the entire White world. Besides the practical problems of achieving and maintaining such an apparently fantastical polity (but, one might argue, no more fantastical than Theodor Herzel’s dream of restoring a Jewish ethno-state on the soil of Ancient Israel . . .), I fear this would be the equivalent of putting all of our European eggs in one basket. All it would take is for the elite of the mono-state to become corrupted or fail, as would inevitably happen eventually, for this to drag the entire race and civilization down. Indeed, the United States of America is precisely such a polity, originally founded as an explicitly White ethno-state, which has simultaneously been corrupted and become hegemonic over the entire Western world.
Given the astonishing diversity of European potentialities — consider the trajectories of the Ancient Greek city-states, the Roman Empire, the Frankish world, the Russian Empire, the British Empire, the United and the Confederate States of America, the German Reich, etc — it would strike me as deeply tragic and stunting for there to be only one political and national form for European Man. While European unity with regard to the non-European world is desirable, ideally I think our interests would be best served by a diversity of great European nations and states, each developing in sovereign and fecund interaction. Darwinian and evolutionary principles support the idea of a diverse European civilization, rather than a single state, which would have the same disadvantages as a single foodstuff (like the potato in nineteenth-century Ireland).
That said, I believe the primacy of European civilizational and genetic interests must be culturally hegemonic across the European World. A Greater European Commonwealth (perhaps akin to the Arab League) should logically include all the countries of Europe and the European diaspora. Finally, at least the nations of Western and Central Europe should be embedded in some kind of polity, for reasons of interdependence, solidarity, and scale (e.g. a continental market and great projects in the cultural, energy, aerospace, and military-industrial spheres). Actually, concerning “Core Europe,” I find the usually rather bland European Commission President Jacques Delors has a rather inspired expression: “a federation of nation-states.”