It seems to me that Russia's strongest precedent for taking Crimea is Georgia's escalation to retake South Ossetia in 2008.
Russia says that Crimea was a region essentially stolen from them and that Russia's conquest was therefore justified as a rescue mission.
While it is ridiculous to assert that Georgia is responsible for the 2008 Russo-Georgia War, Georgia did in fact start the overt fighting after falling into the Russian trap of escalating in response to Russian efforts to destabilize the region and provoke Georgia.
But given Russias conquest of Crimea, wasn't Georgia fully justified in trying to retake a region stolen from them and protect ethnic Georgians trapped in South Ossetia?
Russia's justification for their subliminal invasion and conquest of Crimea actually justifies Georgia's effort in 2008 to restore Georgian control of South Ossetia. Can we at least end the polite fiction that led the West to overlook Russia's 2008 aggression?