There is no legal basis upon which to justify Russia’s recent seizure of the Crimean Peninsula. While Crimea had been a part of Russia until 1954, when then-Soviet leader Nikita Khrushchev transferred control over it to Ukraine, a magnanimous gesture on the part of the ethnic-Ukrainian Khrushchev, that act of transferring it to Ukraine made it officially a part of Ukraine in terms of international law. As such, its seizure by Russian military and security forces constitutes a violation of international law. Additionally, the 1994 agreement by which the government of Ukraine handed over its nuclear weapons that had been stationed there while it was part of the Russian-dominated Soviet Union included a guarantee of its territory integrity by the United States, the United Kingdom, and Russia – and that agreement implicitly included Crimea.
Russian President Vladimir Putin’s justification for the invasion – protection of the Russian-speaking population on the peninsula (about sixty percent of Crimea’s population is ethnic Russian) – would have enjoyed some measure of legitimacy if there had, in fact, been any threat to those Russian-speaking Ukrainians. No such threat existed, and, in all likelihood, Putin used the crisis over the revolt against pro-Russian Ukrainian leader Victor Yanukovych’s tilt towards Moscow at the expense of the European Union to exercise his diplomatic and military muscle – a theory given wide credence in light of Putin’s subsequent thinly-threats against the governments of Moldova and Estonia.
Russian culture includes a deeply-held notion that any territory once under its autonomy remains forever Russian territory. Because the Soviet Union had annexed the three Baltic states of Estonia, Latvia and Lithuania, as well as other regions that came under Russian control over the past centuries, and because Soviet Russian policies had long emphasized the “Russification” of territories added to its empire, including throughout Central Asia as well as Eastern Europe, through the transfer of Russian citizens to settle these occupied territories, Putin is now using the mantra of protecting ethnic Russian populations in each of those countries as an excuse to threaten them with invasion.
To the extent that the actions of United Nations enjoy broad legitimacy with many people, then the votes in the U.N. Security Council and in the General Assembly would certainly seem to delegitimize Russia’s actions. The Security Council, which alone among U.S. agencies or divisions possesses the political authority to compel compliance with its resolutions, voted overwhelmingly against the legitimacy or the Moscow-backed referendum held in Crimea on March 16, 2014. Of the fifteen members of the Security Council, 13 voted against Russia’s action, with China abstaining. Russia, the fifteenth member of the Security Council, and one of only five with a permanent seat on the council and the power to veto resolutions, exercised that authority in blocking passage of the resolution. Symbolically, however, the U.S. Security Council vote was a diplomatic setback for Putin, although a setback with which the Russian leader can apparently live. To conclude, then, Russia’s seizure of the Crimean peninsula has no valid basis in international law, and was not a legitimate seizure of territory, despite the region – including Ukraine’s – historic importance to Russia.
With respect to nations supporting Russia's actions, the list is short, and entirely predictable. Cuba, Nicaragua, Venezuela, and Syria all came out immediately in support of Russia. That each of these countries, especially Cuba, Nicaragua and Syria have long been close Russian allies, with Venezuela a more recent entrant into the world of anti-U.S. foreign policies, is no surprise. More surprising is the recent announcement that the so-called "BRIC" nations are supporting Russia's position. China, the "C" in "BRIC" (the others being Brazil, Russia and India) is, as noted, reluctant to appear at all supportive of Russia's actions given its own tenuous relationships with some of its existing and prospective territories. India, in particular, has long maintained a close military relationship with Russia, and tends to adopt positions that place it at odds with the United States, despite efforts by both countries over the past decade to forge closer ties.
Countries opposing Russian actions include most of the rest of the world. As noted above, every independent country bordering Russia and which used to be part of the Soviet Union, like the Central Asian "stans" (Uzbekistan, Tajikistan, Turkmenistan, etc.) strongly opposes Moscow, although they keep their objections muted out of fear of Russia's military and economic might and their dependence on pipelines that cross Russian territory or run near Russia's borders, making them vulnerable to sabotage. The European Union is adamantly opposed to Russia's actions, as is the North Atlantic Treaty Organization (and there is a substantial overlap between those two entities).