It's probably the good old distraction technique. As long as there's an external enemy, the internal enemies of the people (corrupt government) is spared some pressure. Also military needs to be fed (both litarally at soldier level and metaphorically the corrupt officials, and arms suppliers), so unless you have some "enemy", it's hard to justify all the large training and expenditures.

I'm sure awarding contracts is also good way to siphon out some public money for Kremlin's cronies.