I beg to differ. The only authority that can hold a referendum in Ukraine is Ukraine. Ukraine never held referendums.
There was not a referendum in Ukraine. There was one in Crimea only.
Do you maintain that the only authority that can hold a referendum in
Crimea is Ukraine?
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Did Scotland hold a referendum, or did the UK hold a referendum in Scotland?
I think you will agree, without qualification, that Scotland, not the UK, held a referendum on independence some years ago.
Was this a legitimate refereendum? If the outcome had gone for Scottish independence, would you have accepted it as legit?
So, a referendum was held in Crimea. By, I suppose "Crimea".
Do you still maintain that the only authority that can hold a referendum in
Crimea is Ukraine?
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What deligitimizes the Crimean referendum is not so much the jurisdiction which held it, but the circumstances under which it was held. Chief among them, IMO, the speed and suddenness with which it was pushed through, without first negotiating all the terms and conditions, e.g. for material assets of economic value changing hands. There was no time to fairly inform the population, so it could make an adult choice.
The Scottish referendum was a good example of how this sort of thing is done. Many constitution contain prescriptions for processes of how to alter borders in a democratic process, should the populations (plural!) affected by it be in favor - one could study those.
The Ruscists did none of that.