In a speech before the assembled state legislature of Russia, Russian President Vladimir Putin offered a number of justifications for his invasion and partition of Ukraine.  One of the more chilling “justifications” was this:

Crimea is our common property and a very important factor in the stability of the region.  This strategic territory should be under a strong, sovereign state and that in fact can only be Russia.

And, of course, Russia is the only “strong, sovereign state,” and so Russia can, under this logic, occupy the rest of Ukraine, and it can use this rationale for seizing the Baltic States to the west (a useful set of outlets into the Baltic Sea and thence the world’s oceans), the ‘Stans to the south (a useful buffer against the People’s Republic of China), expand its holdings in Syria (a useful outlet directly to the Mediterranean Sea), and any number of other states who aren’t a strong militarily as Russia, and so can’t be held to be sovereign and whose acquisition might be discovered to suit Russian…interests.