What if a Czar of Russia styled himself Emperor of the Romans, or of the Eastern Roman Empire?
That is linguistically impossible as the Eastern Romans were called "Greeks" in Kievan Rus and later in Russia. That was a strong linguistic tradition.
So no "Roman".
And you can see that "Emperor of the Greeks" or "Emperor of the Greek Empire" is out of the question for many reasons, first of all because it would be laughable for the Russians and for the foreigners.
But no "emperor" as that word was never used in Kievan Rus and in old Russia. And no Caesar. Only Csar or Tsar or whatever you spell it in English - that is an old Slavic name for "Caesar" which was used in Kievan Rus and Russia. For example Constantinople was traditionally called "Tsargrad" as "the City of Tsar/Caesar".
Nothing really. I mean they already considered themselves the Third Rome and heirs of the Byzantine Empire, so besides another grandiose title (that will be ignored by Europe) it won't matter.
That is a widely spread misconception.
It is supposed as an axiom that ALL the Russians were thinking "we are the Third Rome, we are the heirs of the Greek Tsarstvo/Empire".
You'd be surprised that 99,9999% of the Russians never heard of the "Third Rome".
That was a conception of a few literate, learned people, mostly clergy which amused themselves with that idea, toyed with such conception in their pleasure time.
Yeah pretty much this. I mean Tsar meant Caesar in Russian, which pretty much meant Emperor. Not one European monarch recognized this. Calling themselves Emperor of the Romans/ERE would be at best propaganda for the Russians and/or Eastern Orthodox people, at worst he'd be considered crazy by the west (hell probably both).
In the Western Europe conception of the Roman Empire was something that happened with them on their land and which was theirs, known to them, was their history. For the Kievan Rus, for Russia "Roman/Greek Empire" was alien, was something on foreign territory of the foreign people.
When the Russian ruler in Moscow started to call himself "tsar" least of all he thought about the West. Actually he did not think about the East, South, North either. That title was only for internal consumption, for the Russian people inside Russian borders. Grand Prince of Moscow became too powerful and he looked around for a better cool title. Title "tsar" came handy - for more than half of millennia in Rus, Russia "tsar" was a title which meant "strong and glorious ruler". Majority of people with exception of a few learned book worms totally forgot that it derived from "Caesar"; usually the Mongol Khans were called "tsars" by the Russians as they were definitely strong, great rulers.
So when Moscow Grand Prince started to call himself "tsar" ALL Russians understood that as a challenge to hundreds years old Mongol domination - Now our Russian ruler is equal to Mongol "tsars" at last. Something like that.
The Russians did not care how the West would react to such title as "tsar". That was a miner problem of diplomatic translators/interpreters - these learned guys were sure that the right proper translation into European languages was "Kaiser"/Emperor. The Europeans thought it improper due to some funny (from Russian point of view) prejudices and traditions.
And that was never a big problem for the Russian diplomacy, just irritating nuisance.
By the way, a few defeated European Armies by the Russians were enough to convince these European guys that "tsar" meant "emperor". Funny, ain't it?