According to my tv news just now Obama and Putin spoke for 90 minutes by phone.
The tv news stated that;
"Russian troops were welcomed like conquering heroes".
"Crimea is 58% Russian nationals"
"A deal was done some time ago for Russia to have its military in Crimea, and Russian ships use Crimean ports".
This seems to be a civil war rather than an attack on a separate nation...Russia invading Germany for example.
Russia is threatening to invade the main part of the Ukraine which is not Russian nor majority Russian.