> But there was definitely a nation, calling itself and its language Ukrainian, and distinct from the neighboring Russians and Poles, whose statehood mostly dominated over the corresponding territory.

And which state was that? The Cossack Hetmanate? Which rebelled against the western occupiers and eventually joined the modern Russian Empire?

> However, it would be incorrect to refer to that language as "Russian". It was an ancestor language common to modern Russian, Ukrainian, Belarusian, and Rusyn. Historically, wherever that language was spoken, its speakers generally referred to it as "Rusian" (as in "language of Rus"). In Western sources, it is usually referred to as Ruthenian. Conflating it with Russian is one of the tricks played in this kind of propaganda.

So Russian is one of the modern versions of the older Rus language, but isn't? Not sure I follow your logic here, you're pretty much agreeing with me then claiming for some reason Russian doesn't count as being descendant from the older Rusian language.

> Russia claims to be the sole legitimate successor to Kievan Rus, and all other successor states to be "breakaway parts" (ironic, given where Kiev is located).

You're missing a key part of history here: Muscovy, the Cossacks and others all rebelled against various invaders, and formed a common state: the Russian Empire. Which included both Moscow and Kiev for centuries.

> A rough analogy would be if Italy said that it's the Roman Empire

Do you not remember the part where there were a bunch of Italian city states that did eventually rejoin to form the Italian state? Italy wasn't Italy until quite recently. Also, France and Spain were Gaul and Iberia, inhabited by Celtic groups that were invaded by Rome.

This isn't analogous to Russia, Belarus and Ukraine, whose people all came from the same original group.

> This is the point at which then-unified (mostly) East Slavic culture and language breaks apart. Western parts get more exposure to European culture, initially via Lithuania, and later also via Poland when the two form a commonwealth; Catholicism partially (but not wholly) replaces Eastern Orthodoxy, and language gets borrowings from Polish and Latin. Eastern parts get more exposure to the (then mostly Turkic) Mongol culture, with Eastern Orthodoxy becoming even more entrenched per Mongols' usual policy of supporting local religions and using them to control the rulers, and the language gets many Turkic borrowings.

Gotcha, so this is basically the modern revisionist, racist Ukrainian propaganda that Russians = Mongols, and Ukrainians are pure white Europeans, right? Never mind that fact that much of Ukraine (all of Crimea for example, and the south of Ukraine) was ruled by Tatars (one of the offshoots of the Mongol horde) for a decent amount of time. And there was absolutely no intermingling there right? Ukrainians didn't succumb to any Tatar influence or genetics, right?

Edit - also, I'm aware of the entire history of the Rus empire from when the Varangians (Vikings) settled in Novgorod, to when Prince Oleg went from Novgorod to Kiev, to Vladimir the Great, etc... Maybe because my family came during a time long before Ukrainians and Russians were feuding, but even though we've maintained fairly strong Ukrainian identity the modern anti-Russian propaganda is never anything I learned growing up. Just something we see in the media now.