The proximate reason for the controversy is a trade agreement with the European Union (EU) that President Viktor Yanukovych had been negotiating. This pact would have set the stage for eventual EU membership and, for many Ukrainians, genuine modernisation and progress. But Ukraine has remained something of a client state of Russia. For one, the country is the major outlet for the gas that Russia supplies the EU. About half the gas Russia produces flows to Europe through Ukrainian pipelines. Ukraine is also a major buyer of Russian gas and complications over gas pricing have been a permanent source of tension that frequently spill over to Europe. For another, Ukraine owns, thanks to a 1960s "gift" from a sentimental Nikita Khrushchev, the Crimean port of Sevastopol, which remains Russia's main access to a warm-water port (and it is largely Russian managed). Third, Mr Putin's hegemonic vision includes Ukraine in a sort of anti-EU, Eurasian trade union. The benefits of this prospective union have not been apparent to many Ukrainians, since the other two members are Belarus and Kazakhstan.
So it was no surprise that Moscow saw the EU pact as a threat, especially since the pact involved instituting EU-harmonised rules and standards - developments that would not have suited the eastern oligarchs who supply substandard goods to a captive Russian market. The EU pact was also predicated on freeing former pro-EU prime minister Yulia Tymoshenko from jail. It was inevitable that Mr Yanukovych - ousted as prime minister in the 2004 Orange Revolution but elected president in 2010 in a heavily rigged poll - would succumb to Mr Putin's blandishments of cheaper gas and a $15-billion bailout to walk away from the deal. But neither he nor Mr Putin bargained for the protests persisting. When none of Mr Yanukovych's half-hearted concessions proved acceptable, a bloody crackdown followed but the tide of popular opinion was too strong for the strongman. Now, with an absconding president, a speaker in charge of Parliament and persistent turmoil in Kiev's Maidan, much depends on what Mr Putin does next. Will he cause Ukraine to split along ethnic lines? It is worth wondering whether Mr Putin has overreached himself this time. After all, Ukraine has a recent history of independent thinking: it was the first of the republics to vote to break away from the old Soviet Union in 1991.