The crisis in the Ukraine was provoked last fall when Yanukovych reconsidered earlier moves toward integration with Europe. He is from the east of the country, which has many ethnic Russians and which is economically, culturally and historically deeply entwined with Russia. The offer by Russian President Vladimir Putin of $15 billion in aid helped to make Yanukovych's mind up. In my view US aggressiveness in the past 23 years is part of the problem here. The US insisted on expanding NATO by absorbing former Warsaw Pact members and humiliating Russia. The rise of Putin is in part a reaction against that humiliation. Russia is reasserting itself as a great power, carving out spheres of influence in the old 19th century way. Ukraine, Kazakhstan and Syria are in those spheres of influence. In the 19th century, wars often were caused by one country not respecting another's proclaimed spheres of influence. Both liberal and right wing youth in the west of Ukraine as well as in the southern capital of Kyiv (Kiev) were upset by the turn away from Europe. They hope for Ukraine to become a member of the European Union and entertain hopes that this step would improve their economic prospects. (Given the sad economic state of Spain, Greece and other EU members, including persistent unemployment of a quarter or more of the youth, this conviction is a little difficult to understand). The more extreme nationalists are reacting against what they see as Russian dominance (a mirror image of right wing Greek politics, which is anti-liberal and anti-EU).
It's messy. And it is not as simple as "protesters are good". A lot of the protestors are right-wing fascist goons.