~Are you speaking of Crimea, or this area of E. Ukraine?~
Forget about Crimea. How could they ‘invade’ Crimea given it is a base for a Russian Navy and it was allowed to move and station up to 25,000 troops there.
We are talking about mainland Ukraine.
Crimea was mainland Ukraine until a couple months ago
The area of E. Ukraine has Russian-trained insurgents, trained in Russia (by admission of rebel leaders), and Russian equipment crossing the border (as observed by Reuters and others).
So let's not muddy the water.