What is there to assault in the Crimea? I think that Ukraine has one infantry brigade and no armor in that region, backed up by perhaps one squadron of aircraft. It's a pretty "safe" bet by the Russians as not much is going to challenge them.
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You're assuming their targets are military. Sometimes it's girls. Here we have Russian anti-fascist liberators in action in 1991. Let's hope their tanks don't run over any girls this time.