http://www.merriam-webster.com/dictionary/annex Simple Definition of annex : to add (an area or region) to a country, state, etc. : to take control of (a territory or place)
There is a big difference between separation and annexation.
In general, do we have many examples of countries changing borders forcibly after some time mid-last century? I certainly don't remember such a thing from G7. In this light, annexation of Crimea stands out as a regression to older - and less civilized by some standards - ways of doing things.