PART I So first I want to back up a bit and quote the entire passage in quesiton:

"Ad vocem Poland, I was most interested to read the work by Elias Regnault (the same who wrote the ‘histoire des principautés danubiennes'), ‘La Question Européenne, faussement nommée La Question Polonaise’. I see from it that Lapinski’s dogma that the Great Russians are not Slavs has been advocated on linguistic, historical and ethnographical grounds in all seriousness by Monsieur Duchinski (from Kiev, Professor in Paris); he maintains that the real Muscovites, i.e., inhabitants of the former Grand Duchy of Moscow, were for the most part Mongols or Finns, etc., as was the case in the parts of Russia situated further east and in its south-eastern parts. I see from it at all events that the affair has seriously worried the St Petersburg cabinet (since it would put an end to Panslavism in no uncertain manner). All Russian scholars were called on to give responses and refutations, and these in the event turned out to be terribly weak. The purity of the Great Russian dialect and its connection with Church Slavonic appear to lend more support to the Polish than to the Muscovite view in this debate. During the last Polish insurrection Duchinski was awarded a prize by the National Government for his ‘discoveries’. It has ditto been shown geologically and hydrographically that a great ‘Asiatic’ difference occurs east of the Dnieper, compared with what lies to the west of it, and that (as Murchison has already maintained) the Urals by no means constitute a dividing line. Result as obtained by Duchinski: Russia is a name usurped by the Muscovites. They are not Slavs; they do not belong to the Indo-Germanic race at all, they are des intrus [intruders], who must be chased back across the Dnieper, etc. Panslavism in the Russian sense is a cabinet invention, etc.

I wish that Duchinski were right and at all events that this view would prevail among the Slavs. On the other hand, he states that some of the peoples in Turkey, such as Bulgars, e.g., who had previously been regarded as Slavs, are non-Slav."

From this passage we can see that Marx is discussing the writings of Franciszek Duchinski, who is a quite interesting figure, albeit one who has not much written about him in English.

Duchinski was born in 1816 to an impoverished Polish-speaking szlachta (noble) family living in Right-Bank Ukraine, ie the part of Ukraine just to the West of the Dniepr River. He was educated at secondary schools before moving in 1834 to Kyiv, where he became a tutor to Polish-speaking aristocratic families. He left the Russian Empire via Odessa in 1846, and eventually arrived in Paris, where he attached himself to the Polish emigre community there, notably Prince Adam Czartoryski (specifically Duchinski worked and interacted with other Polish-speaking emigres from Right-Bank Ukraine who worked with Czartoryski). Anyway, Duchinski worked as Czartoryski's agent in Italy, Serbia, and in Istanbul, where he even served as a civilian consultant to British forces during the Crimean War. He eventually returned to Paris and published a vast number of scholarly articles in French and Polish, as well as giving public lectures, especially on the topic of Polish-Ukrainian cooperation. He moved to Switzerland in 1872 and became director of the Polish National Museum outside of Zurich, and died in 1893 (his epitaph is written in Ukrainian transliterated into Polish) .

So for someone connected to the Parisian intellectual scene in 1865, Duchinski would be a well-connected public intellectual who would be familiar. However, as Ukrainian historian Ivan Rudynytsky would write about Duchinski,"as a self-taught man with a one-track mind, he was by no means a sound scholar. Duchinski did not hesitate to bend facts to make them conform with his preconceptions."

So, on to the theories in question. Duchinski strongly believed in a division between Indo European "Aryans" and "Turanians". The latter group is pretty immense - into this group he included Finno-Ugrians, Turks, Chinese, Semites, Sub-Saharan Africans, American Indians, and Australian Aborigines. The main difference between the former and the latter was that Aryans were sedentary agriculturalists, and Turanians were nomads - this difference impacted all aspects of social and cultural life, and were ineradicable. Of course we shouldn't be surprised that in Duchinski's theory the Aryans were imbued with a love of freedom and a strong intellectual capacity, and the Turanians were incapable of this.

Because of his personal origins and his politics, Duchinski applied this theory to Polish-Russian relations, seeing Ukraine as the key battleground in what was effectively a racial war. What is now Ukraine (west of the Dniepr), Belarus, the Baltic, and Smolensk area (ie, the former Polish-Lithuanian Commonwealth), plus the former Republic of Novgorod was all a racially-unified area opposed to the "Turanian" Muscovy of the Volga Basin. In Duchinski's words: "The Muscovites are neither Slavs nor Christians ... they are nomads to this day, and will remain nomads forever." In his view "Muscovy" had usurped the name "Rus'" (which more properly referred to Ukraine), and the people there were closer to Chinese than to Belorussians or Ukrainians. Ukrainians and Belorussians in turn were closer to Irish or Portuguese or to white Americans than to "Muscovites".

The basis for these claims is that Duchinski was arguing that, in effect, the people of Russia were Slavicized Finno-Ugrians- they may be speaking a Slavic language, but racially were not Slavs. There is a small kernel of historic fact here in that Russian history did indeed involve a fair amount of linguistic and cultural Russification of non-Slavic peoples in European Russia, including Finnic speakers, Ugrians, Balts, and Turkic peoples. But Duchinski is obviously spreading in a heavy dose of scientific racism here, and also arguing that no Slavs actually migrated to what is now Russia in this process. So the acculturation is all superficial - Duchinski impressively argues that Muscovites are too autocratic and too communistic to ever become democratic federalists, because of their basic nomadic nature (unlike the Polish-Ukrainian Rus'). As a result, in Duchinski's retelling, there has always been war between Muscovy and Rus', and always has been organic unity between Rus' and Poland - he sees Polish and Ukrainian as closer than Polish is to Czech and Ukrainian is to Russian, and while you can find such commonalities most linguists would not accept this.

As Rudynytsky puts it: "Duchinski dealt ingeniously with historical facts not easily reconcilable with his vision of a providential Polish-Ukrainian harmony." Basically - if Polish-Ukrainian history ever shows conflict, it's Turanian fake news. The Khmelnytsky rebellion against Poland? Ukrainian Cossacks are actually Tatars who oppressed Ukrainians. The Cossacks who revolted under Ivan Mazepa against Peter the Great? Those Cossacks are Aryans.

Duchinski was above all a Polish speaker, but saw Ukraine as having a place in a restored Poland along the lines of the unsuccessful 1658 Treaty of Hadiach, which would have put the country on equal footing with Poland proper. He was enthusiastic about the Ukrainian national revival, although technically speaking he wasn't part of it. This could get a little weird in his view of contemporary cultural figures - he argued that not only Taras Shevchenko but Nikolai Gogol was not a Muscovite but a Ukrainian. Both were born in Ukraine, but identifying Gogol as an anti-Muscovite Ukrainian nationalist is a bit of a stretch, to say the least.