[Travis McGee]

What my 1914 map above shows is that Central Europe's countries and borders appear, disappear and shift constantly, like sandbars.

Do you know what "Ukraine" translates as in Polish, Ukrainian, and Russian?

Borderland. That's why it was called THE Ukraine, that is to say, "The Ukraine" denominated a borderland region, not a sovereign nation, not until 1991 and the breakup of the USSR.

[Thunder90]

The thing is that the Soviet Union was seen as “unbreakable”. Also, Putin sees the break up of the USSR as illegal and illegitimate.