Why Russia should not attack Sweden?
medium.com
medium.com
...like Ukraine over Crimea.
Of course they won't invade Finland or Estonia or Poland or Latvia or Lithuania, because the treaty says NATO may intervene (though it's not guaranteed).
But we still need some international millitary force for stabilization US-or-otherwise invaded regions.
Can you even find a significant number of Crimeans that are unhappy with the situation ? If Crimea had really been invaded by Russia where are all the testimonials of the Crimeans saying that their life is worse than before and that they wish to go back to Ukraine ?