Leaving aside the question of foreign powers backing one side or the other, it's an interesting philosophical question : the legitimacy of revolution, the legitimacy of secession.

A possible analogy is the American civil war : certain regions reject the democratically-decided changes (political association with the EU / abolition of slavery, respectively).

The unrest in Donbas was triggered by the Maidan revolution; many people there, and in other cities in the south and east, were pro-Russian, and rejected a change to the status quo (i.e. de facto Russian domination of Ukraine). It is interesting to note that the military revolt in the Donbas was preceded by the seizing of Crimea by the Russian military (which was, in itself, an explicit reaction to the loss of Russian hegemony over Ukraine).

I don't know whether the Donbas militias were waiting for this implicit proof of Russian backing before starting their war of secession, or whether they were awaiting orders from Russia. Do you?

_{It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II}