It makes sense to annex territory that welcomes you. That’s why Crimea went off without a hitch. And so, perhaps, Donbas, too. But Kiev? There would be an insurgency. And the West would supply it. And who would want that? So it’s the Donbas or just a bit of fun watching the West sweat. Either way, the Orange Revolution will still have left the West way, way ahead on this one, for Russia’s longstanding, historic buffer zone (“krain” is a slavic word for a march, and a march is a borderland) will still mostly be on the West’s side. At least for now.
One is struck by how unlike 1939 the situation really is.
Back then, Russia’s buffers were buffers against Germany, and those same buffers were also Germany’s buffers against Russia. And the West, in the sense of Britain and France, did not border those buffers at all. When Poland (the buffer at issue back then) sided with the West, it had no prospect of support across a land border.
In siding with the West, Poland became of no value to either Germany or Russia, each of which would otherwise have wanted to support it as a buffer against the other. Instead of being a friend of one and a threat to the other, Poland became a threat to both. And so the two powers got together and agreed to divide Poland between themselves via the secret protocol to the Molotov-Ribbentrop Pact.
The West could not oppose this by fomenting trouble in-country—as it certainly can do with Ukraine today—because the West had no land borders with Poland across which to run supplies. To stop it, the West had to go to war. Which it did. Although it never did succeed at saving Poland.
But today, Germany, defeated in the Second World War, is now with the West. And Poland is now with the West. And Russia is down to its last buffers, Belarus and Ukraine. And Ukraine wants out. And has plenty of friends on its western borders.