Moscow gave Crimea to Ukraine three times. That wasn't enough to seal the deal?
I know that apologists for Russia's invasion of Crimea like to say that the Soviet Union giving Crimea to Ukraine in 1954 was kind of a kooky mistake that shouldn't have been made. Ukraine was the Ukraine then, and part of the Soviet Union. So, they say, it was an administrative formality that should have no real effect on our 21st-century thinking.
Although some people (and especially Russians) like to say that Ukraine isn't a real independent state apart from Russia, remember that Ukraine is a founding member state of the United Nations, joining on the same date as America, Britain, and Russia (as the successor state to the USSR), among others. Stalin did make Ukraine a member state of the United Nations.
I understand that Ukraine's UN membership was just a Russian ploy to get each Soviet republic its own UN seat--which President Roosevelt blocked by saying America would want 48 seats, if that was the case. We compromised on giving Russia 2 more for Belarus and Ukraine confident we had the Latin American states' votes locked up. So hey, we both made mistakes in the long run. Tough.
The bottom line is that Stalin did give Crimea to Ukraine--which Stalin had insisted a decade earlier was a member of the United Nations separate from the USSR.
Russia could have addressed this "error" of Stalin giving Crimea to Ukraine after the collapse of the Soviet Union in 1991. When the territory of the old Soviet Union was apportioned among the successor states, Russia did not object to Crimea remaining within Ukraine. And Crimeans even voted (narrowly) to stick with Ukraine rather than go with Russia.
And then Russia confirmed the territory issue for a third time when they guaranteed Ukraine's territorial integrity--which includes Crimea--with the 1994 Budapest Memorandum that granted that protection in exchange for Ukraine giving up their nuclear weapons inherited from the Soviet Union. I guess getting Kiev to give up Crimea in 1994 wasn't as important. They were right, of course, as the last couple weeks have demonstrated. By the end of this month, Ukraine will have neither nukes nor Crimea.
Wait. What? Is the saying "fourth time's a charm?"
It's almost as if you can't trust the Russians to keep their word. Trust but verify, indeed.