He mentions the importance of history of the region etc. I suppose what he means is the ethnic Russian population.
You know, every single census since the Russian Imperial census of 1897 - and including the Soviet Union census of 1926, as well as the Ukrainian census of 2001 - show that ethnic Ukrainians - not Russians - have always been the majority in Eastern and Southern Ukraine.
I think that all of this propaganda about Russians being the majority there, is based on 2010 election results.
They claim that voting for Yanukovych in 2010 = being ethnic Russian and voting for Tymoshenko in 2010 = Ukrainian. That would be like saying that Poland is also divided 50/50 into two ethnic groups, because half of Poland votes for Kaczynski & Co. and half for Tusk & Co.
This war has revealed the falsity of that propaganda - we are not seeing crowds of Russians welcoming Putin's tanks with flowers.
The main argument is actually the confession first and dialects second as far as I understand it. As well as a general identity different from the West. Obviously, many Western regions are in many ways closer to Poland-Slovakia, from genetics to culture, than the Eastern ones. Basically, from a religious-ideological point of view, there are two splits in the Ukraine, Catholic vs. Orthodox and within the Orthodox Christians, between those belonging to the Ukrainian church vs. the Russian one.
Especially the switch to the Ukrainian church was kind of a political statement in the Ukraine, and the frequency of this is quite obviously regionally split, note where the hotspots are:
https://static.cambridge.org/binary...0:S0010417519000410_figU1.png?pub-status=live
These are also the regions which were for a longer period part of a more Western state (Poland-Lithuania) and acted differently during World War II and will now, I would assume, resist more and recruit more volunteers for the war.
Probably the Russian aggression changes the attitude of the Easterners too, but before this invasion, the differences were fairly obvious.
Its in any case interesting to compare the above map of communities which switched to the Ukrainian orthodox church with the dialects of the Ukraine:
https://qph.fs.quoracdn.net/main-qimg-f442a17b854045c5d305cc82b7007987
Votes in the ominous election before the conflict got violent:
There is a clear overlap of ethnolinguistic, religious-ideological, historical and geographical borders. We can clearly see that there is a heartland for the Ukrainian nationalism and resistance, which is in the West of the country. And a more pro-Russian, Eastern affiliation in the East.
How the invasion changes that is the great unknown, because large portions of the Eastern people might come to terms with Russians more easily, or they might unite against what might be seen now as a common enemy and aggressor.
That's one of the big unknowns in this war, also for the Ukrainian and Russian leaders I guess, how the Eastern inhabitants of the Ukrainians, beyond the more clearly pro-Russian Donbas, will react to this and how the war changes their attitudes.
Probably someone is not happy with the dialectal/ethnolinguistic map, but the basics don't change in other maps with "less Russian", the North West is the core zone for the Ukrainian nationalism and resistance, the very East for the pro-Russian base and sentiments. It always was. Basically, the pro-Western and anti-Russian sentiment is the strongest in the part of the Ukraine which was once a part of the Polish kingdom, the overlap is nearly 100 %:
The lower the historical connection to the West (mostly Poland), the lower the support for the Ukrainian nationalism. And this dates back to times long before this conflict.
