But that's _literally_ how a bunch of countries split from other countries. In a different context, we might celebrate it and call it "gaining independence" or "reuniting with their motherland".
However, if it's not annexation it's probably better described as "ceding"; an American example: France ceded Louisiana to the United States by the treaty of Paris, of April 30, 1803. Spain made a cession of East and West Florida by the treaty of February 22, 1819.
Cessions have been severally made of a part of their territory by New York, Virginia, Massachusetts, Connecticut, South Carolina, North Carolina, and Georgia.
Crimea is a special case: it used to be Russian but was reassigned to the Ukraine at the time when they both were part of the USSR. It wasn't a big deal until the USSR dissolved and suddenly Crimean residents turned out to be in a foreign country.
It had been Turkish before it was Russian. Should we go on?
Besides, the indigenous population (Crimean Tatars) and the Ukrainians in Crimea never thought of Ukraine as a foreign country.
Let's not confuse events of the 18th century and the modern history.
Crimea was called Crimean Khanate at that time and the backbone of its economy was the slave trade. As a major slave trade hub it has seen many hundreds of thousands of Russians and Ukrainians captured by Crimean Tatars and sold to Turkey until Catherine the Great's counter-terrorist operation finally put an end to it in 1783 :)
This dramatic history rooted in inability of the Crimean Khanate peacefully coexist with Russia can hardly be compared with a single action of a Soviet bureaucrat in Moscow in 1954.
And you are misinformed, Crimeans Tatars are not the indigenous population, they are a remnant of the Golden Horde.
Yes, I was off with the numbers, so I had deleted my comment just before you replied to it. But the point is still valid: the current ethnic composition of Crimea was greatly affected by the deportation.
You're totally right. Think about it, British/French/Spanish/... move to somewhere near grand canyon, do a referendum and they proclaim it United States? Ridiculous!