Powerful images have been pouring out of Ukraine lately: Kiev's Maidan protesters bravely enduring months of bitter cold, withering police attacks, and sniper bullets; the gilded bathroom fixtures of deposed President Viktor Yanukovych's opulent personal residence; a wheelchair-bound Yuliya Tymoshenko emerging from prison to address her countrymen. And now Russian troops in Crimea's cities.

At a time when Europe's self-confidence is at low ebb, Ukrainians' courageous struggle to topple a rotten political system is a powerful reminder of Europe's core values. The question now is what Europeans will do about it.

With the Russian Duma's approval of President Vladimir Putin's request to use Russian military forces in Ukraine (not restricted to Crimea), the mirage that Yanukovych's ouster signals the start a new era, in which Ukraine moves inexorably away from Russia and into the European democratic fold, has now evaporated. Confronted with a reality that they should have foreseen, Europe's leaders must recognize that Ukraine is subject to deep internal cleavages and conflicting geopolitical forces.