The Crimean war

As the Mongol Khanate of the Golden Horde began to fragment, one of its successor states was the Khanate of the Crimea.  This came to cover most of what is modern Ukraine.  In the 15th century, if fell to vassal status under the rising Ottoman Empire.  As Moscow began its steady rise, the territory of the Crimea was chipped away until in 1783 the Khanate was annexed outright by Russia under Catherine the Great.  In 1954, Nikita Krushchev, in a romantic gesture commemorating the 900th anniversary of the death of Yaroslav the Wise (a famous leader of the Kievan Rus), handed administration of Crimea to the Ukrainian Soviet Socialist Republic, never thinking for once that the Soviet Union would collapse before pure communism was realised.  And so we are at the pretty pass today.
Under the terms of the 1994 Budapest agreement, where Ukraine swapped its Soviet-era nuclear weapons for Russia guaranteeing its economic and territorial integrity, Russia was allowed to station 25,000 troops in the Crimea.  The Kremlin is taking full advantage of that clause but by occupying government buildings and airports and severing the internet and phone connections with Ukraine north of the Perekop isthmus it is violating all the other clauses of the settlement.  Russia is just itching for Ukraine to start a fight with it and exercising maximum provocation.  The new interim government's decision to rescind a language law that made Russian a second official language in area where the majority were ethnic Russian was coarse and unnecessary.  But it was exercising its right as a sovereign state.
The Kremlin is indulging in its usual Orwellian double-speak.  Dmitry Medvedev said Russia was ready to develop links with Ukraine but not with "those who seized power through bloodshed."  The blood was shed by Viktor Yanukovych's decision to start shooting unarmed protestors, on orders from Moscow, so if Medvedev had an honest bone in his body that would mean Yanukovych.  However, since stepping down as president, Medvedev is a busted flush with as much freedom as a ventriloquist's dummy.  This is the most brazen attempt to take over territory by a major power on the question of minority rights since the disastrous Munich Conference over the Sudeten Germans (which prompted the United Nations to drop the promise of the League of Nations to protect 'minority rights' and replace it with a promise to protect 'human rights').  Comparisons with the Nazis are often risible but I can think of no other parallel in the intervening 70 years (unless one references the seizure of Memelland from Lithuania in 1939) on the question of minorities prompting a land grab - a despicable act but distinct from the more heinous crimes of the Nazis, so I think the parallel if justified.
Russia has form.  It sent in 'peacekeepers' to separate the Moldovans from the renegade Transdnistrian Republic.  They were supposed to leave once they had decomissioned a major military base in Transdnistria (with its majority ethnic Russian population).  The base is still there, as are the 'peacekeepers'.  Russian peacekeepers are still in Tajikistan after ending the civil war there.  And they are there on 20% of sovereign Georgian territory, protecting the breakaway regions of Abkhazia and South Ossetia after Georgian president Mikheil Saakashvilli walked into the trap set by Moscow's provocation and attacked South Ossetia's capital, Tskinvali.  This was nothing to do with Abkhazia but that wasn't going to stop Russia.  And so, a referendum to secede is set for the 28th May, the same day as national Ukrainian elections and the result will be rigged so that it is answered in the affirmative.  Then Russia can either annex it outright or treat it like Abkhazia and South Ossetia, which along with only four other countries it treats as independent states (only in Transdnistria has Russia withheld its recognition).
The revolution in Kiev was bottom-up - a few nationalists to serve as muscle but mostly ordinary citizens angry at the looting of the country and increasing authoritarian character of Yanukovych.  The revolution in Crimea is top down - directed from Moscow and carried out by Russian special forces.  If Kiev's interim government take any military action, the Donetsk region too could be snatched away.  For Vladimir Putin, payback over Kosovo is never-ending.  If there is to be a more low-level Cold War (without the threat of thermonuclear destruction) as Sir Malcolm Rifkind says, then Putin will take the lion's share of responsibility for that.