“Well, 90% of Crimeans wanted to be Russians”
This is correct.
Crimea was part of Russia longer than longer than the U.S. was a country. Kruschev—a Ukranian—”Gave” Crimea to the “state” of Ukraine without obtaining consent of their Parliment (?) which was supposed to approve all changes in borders/land swaps etc. It just returned to its original country / borders. No reason to send the U.S. Army pouring thru the Fulda Gap!
Crimea and Ukraine were both part of the Soviet Union when Kruschev “gave” Crimea to Ukraine. They were still just parts of the USSR. Now Russia and Ukraine are different countries. Most of the people in Crimea are of Russian ancestry.