It all depends on how far back you want to go. Before the annexation, there was a referendum, but before the referendum, there was de facto occupation by the "polite people" aka Russian forces with all identification tags removed (a war crime in and of itself, by the way).

Before the occupation, there was Maidan. And before Maidan, there was Yanukovich, whose achievements include stuffing the Supreme Court, and having it scrap the country's new 2004 Constitution and reverting to the old one, which, coincidentally, gave president a great deal more power than the new one.

We can go all the way back to Pereyaslav Rada if you want, but what's the point of the exercise? No matter how you slice it, Russia invaded and occupied a part of a sovereign country, and there was no genocide or other serious crimes against humanity ongoing there that could possibly justify such a thing.

If you stop at "Before the occupation, there was Maidan", then do a serious investigation of those behind the Maidan, you'll get the real answer.

Hints: John McCain went to egg them on (He was in Libya and Syria too). The US ambassador was handing out cookies to police officers. And then there's Victoria "Fuck the EU" Nuland - http://www.bbc.com/news/world-europe-26079957

So what? Last I checked, there were Russian tanks in Crimea and Donbass. There were no US tanks in Kiev.

Or are you saying that tanks are an adequate response to cookies?

Whatever happened in Ukraine before the annexation of Crimea has absolutely no any relationship to Russia.

Putin once again failed in his attempt "to restore" USSR via more "peaceful" means 2nd time in a row was a bit too much for him so he snapped setting Russia on course which will likely bring the collapse of Russia similar to that of the USSR.