Ehhhhhh.........what?
Regardless, Ukraine asked for help. Obama did not help them militarily. Crimea was gone.
Ukraine and Russia were both members of the Union of Soviet Socialist Republics. Crimea was part of the RSFSR (Russia).
In the 1950s, in recognition of Ukraines suffering in the war and for who knows what else, the USSR government took Crimea from Russia and added it to Ukraine.
Back then, all people involved were Soviet citizens first and foremost so the practical effect of the move was little.