Nato's relentless push to isolate and encircle Russia made this all but inevitable once Western Ukraine signalled that it too would join Nato and EU.
It seems Russia is intent on seeing an independent state formed east of the Dneiper, which would be in the Russian sphere. In fact it might be looking to create dissension amongst the large Russian populations in the Balkans to establish other buffer states against Western encroachment.
In fact Russia, even in the time of the Soviet Union has never really been interested in Empire. It's foreign policy has always been predicated on establishing a ring of States around the Russian heartland, within its orbit, and supporting its economic interests.
It was very near sighted of the West to declare itself the 'winner' of the Cold War, when Communism collapsed, and not see that the deep cultural differences and suspicions between the oriental sensibilities of Russia and those of occidental Western Europe remained. They went headlong into expansionism eastward, exasperating Russia's paranoia of Western intrusion, and a push back was inevitable.
Russia won't invade the Ukraine, but it will enable the separatist forces in the east. Since ethnic Russians form the majority there, that is likely all they'll need to prevail within their limited objectives.
