ok...
long story cut short :
1) 1917 russian revolution , crimea became part of ussr.
2) 1924 , stalin came in...
3) 1932 , famine in ukraine..
4)after ww2 , deportation of tatars from crimea replacing them with russians.
5) 1954 crimea tranfered from russian-ssr to ukraine-ssr..
6) 1991 ussr...