A geopolitical bastion of Russia
The Crimean operation was a response to the threat of NATO's further expansion along Russia's western border. By this logic, Putin seized the peninsula to prevent two dangerous possibilities: first, that Ukraine's new government might join NATO, and second, that Kiev might evict Russia's Black Sea Fleet from its long-standing base in Sevastopol. ... Putin's seizure of Crimea appears to have been an improvised gambit, developed under pressure, that was triggered by the fear of losing Russia's strategically important naval base in Sevastopol.
Russia's Black Sea Fleet
The Crimean port of Sevastopol, home of the Black Sea fleet, is vital to Russia's naval power in the Mediterranean and beyond.
International legal bodies regard the result of successful break-ups the way friends see a separating couple: as two newly unlinked individuals, like it or not. So if Russian-speakers in Crimea (which already has the status as an "autonomous republic") vote to slice themselves off from Ukraine next week and throw themselves into the arms of the Russian Federation, no international court will raise much of a fuss.
According to Primary Right Theories, a group can have a (general) right to secede even if it suffers no injustices, and hence it may have a (general) right to secede from a perfectly just state. ... Similarly, according to Associative Group Theories, what confers the right to secede on a group is the voluntary choice of members of the group to form an independent state.
Western states have quite openly and strongly used the creation of an exemption to rules of international law as an instrument that was at least also beneficial for their political interests. Russia now is denied the same right though the Crimean population's demand to accede to Russia is — as a matter of politics not law — not unjustified, given the apparent majority opinion there.
A Crimean man makes the "victory" sign as he celebrates on Simferopol's Lenin Square after polling stations closed in the Ukrainian republic on March 16, 2014.
Russian is also spoken widely and is the mother tongue of many Ukrainians, especially in the east and in the southern region of Crimea, where ethnic Russians are in the majority. Violent protests broke out in the Crimean capital of Simferopol on February 27, against the new order set in motion a week earlier amid mass demonstrations in the country capital of Kiev. Crimea is a bastion of support for ousted President Yanukovych.
Polls by Western firms suggest the opposite: Crimeans in 2015 are even more accepting of the accession to the Russian Federation than they were in 2014.
I would like to say that Russia has not annexed anything. Everything that has happened in Crimea is the result of illegitimate actions by certain political forces in Ukraine who provoked a coup d'état. As for Crimea, it joined Russia based on the expression of the will of the people living in this territory.
Vladimir Putin - Beginning of the expanded format meeting of the CIS Council of Heads of State (September 16, 2016)