(Thanks to Mr C. for pulling together these quotes by Leontiev.)
«... A state grouping according to tribes and nations  is.. nothing other than the preparation - striking in its force and vividness - for the transition to a cosmopolitan state, first a pan-European one, and then, perhaps, a global one, too! This is terrible! But still more terrible, in my opinion, is that fact that so far in Russia nobody has seen this or wants to understand it...» «A grouping of states according to pure nationalities will lead European man very quickly to the dominion of internationalism.» 
Leontiev based his apparently paradoxical thought on the fact that the very striving of the nations for «liberation» within the bounds of national states was dictated by their striving to be like everyone else: «... having become politically liberated, they are very glad, whether in everyday life or in ideas, to be like everyone else». He produced an example: for a man who has been released from prison, it is not a matter of indifference at what time they released him. If there is an epidemic raging at that time, it would be safer for him to remain in prison. And so, too, «the political nationalism of our time does not give national isolation, because the overwhelming influence of cosmopolitan tastes is too strong. The epidemic has not yet come to an end.» 
Although they appear to be opposites, there is in fact a close kinship between ecumenism and nationalism. This kinship was elucidated by the Russian diplomat and publicist Constantine Leontiev, who, though an ardent philhellene, was strongly critical of the nationalism of the Greek revolution. He also thought that the Serbian and Bulgarian nationalisms that motivated the other Balkan revolutions were very similar in their aims and psychology to the Greek – that is, sadly lacking in that "universalist nationalism" that he called Byzantinism. These petty nationalisms, argued Leontiev, were closely related to liberalism. They were all rooted in the French revolution: just as liberalism insisted on the essential equality of all men and their "human rights", so these nationalisms insisted on the essential equality of all nations and their "national rights". But this common striving for "national rights" made the nations very similar in their essential egoism. It replaced individuality with individualism, hierarchy with egalitarianism, right faith with indifferentism (ecumenism).
Leontiev believed, as Andrzej Walicki writes, that "nations were a creative force only when they represented a specific culture: 'naked' or purely 'tribal' nationalism was a corrosive force destroying both culture and the state, a leveling process that was, in the last resort, cosmopolitan; in fact, nationalism was only a mask for liberal and egalitarian tendencies, a specific metamorphosis of the universal process of disintegration". According to Leontiev, the nations' striving to be independent was based precisely on their desire to be like every other nation: "Having become politically liberated, they are very glad, whether in everyday life or in ideas, to be like everyone else". Therefore nationalism, freed from the universalist idea of Christianity, leads in the end to a soulless, secular cosmopolitanism. "In the whole of Europe the purely national, that is, ethnic principle, once released from its religious fetters, will at its triumph give fruits that are by no means national, but, on the contrary, in the highest degree cosmopolitan, or, more precisely, revolutionary." The revolution consisted in the fact that state nationalism would lead to the internationalist abolition or merging of states. "A grouping of states according to pure nationalities will lead European man very quickly to the dominion of internationalism" - a European Union or even a Global United Nations. "A state grouping according to tribes and nations is… nothing other than the preparation - striking in its force and vividness - for the transition to a cosmopolitan state, first a pan-European one, and then, perhaps, a global one, too!..."
Holy Ælfred the Great, King of England, South Patron, pray for us sinners at the Souð!
Anathema to the Union!