Widening rifts over Ukraine
The bloodshed in Ukraine carries the risk of intensifying rifts, both internally and internationally.
Inside Ukraine, even if the protests are more complex and interwoven than a neat divide between East and West, the violence could easily radicalise people, pulling them in different directions.
Internationally, too, a chasm is opening between Russia and Western powers, with potentially broad repercussions. It may not be entirely clear who is to blame for inflaming the situation this time, but the responses from major powers, East and West, represent a stark divergence.
The Kremlin has allied itself unequivocally with President Viktor Yanukovych. The Russian foreign ministry described the violence as an "attempted coup d'etat" and demanded that opposition leaders in Ukraine "stop the bloodshed".
President Vladimir Putin has been in touch with Mr Yanukovych by phone. Kremlin spokesman Dmitry Peskov was careful to insist that the Russian president did not offer advice, but added that Ukraine was a "friendly brotherly state and a strategic partner" and Russia would use all of its influence to restore peace and order.
By contrast, Western leaders have sided with the opposition.
In the United States, the focus has been on trying to persuade Mr Yanukovych to pull back government forces and exercise restraint. US Vice-President Joe Biden reportedly got through to him on the phone, and suggested he bore special responsibility to "de-escalate" the situation and address the protestors' "legitimate grievances".
In Europe, Swedish Foreign Minister Carl Bildt went so far as to say that President Yanukovych had "blood on his hands".
German Foreign Minister Frank-Walter Steinmeier said Ukraine had "paid dearly" for the president's "delaying tactics" in refusing to hold serious talks about conflict resolution.
Polish Prime Minister Donald Tusk said the Ukrainian authorities had lost their democratic mandate.
A range of EU countries, including France and Germany, are now calling for targeted sanctions to be imposed on Kiev as a gesture of solidarity with the Ukrainian people. An emergency meeting of EU foreign ministers has been called for Thursday to discuss it.
This is the first time the EU has raised the prospect of sanctions against President Yanukovych's government. Until now the focus has been on trying to mediate between the opposing sides, and urging President Yanukovych to rethink his rejection of closer trade ties with the EU and an IMF-supported bailout. So this is a significant shift in Europe's approach to the crisis.
But it is hard to see how the imposition of sanctions could make much difference, beyond forcing President Yanukovych to turn his back on Europe for good.
Rickety diplomatic bridge
Similarly, there are good reasons for Mr Putin not to be seen to get involved in any wider security crackdown in Ukraine. Experience has shown that interventions by Moscow, whether political, economic or otherwise, tend to intensify any backlash against Russian influence.
What happens in Ukraine next may depend more on attempts at mediation by former Ukrainian politicians and powerful local oligarchs, desperate to avoid worsening violence.
But internationally the tensions could still reverberate.
For some time there has been an uneasy truce between the Kremlin and Western powers. On questions like Ukraine they have accused each other of meddling, but have agreed to disagree. On other questions, like diplomacy over Syria or Iran, they have tried to collaborate.
But there seems to be little trust between the two sides, and efforts at diplomacy are fragile, as the recent collapse of Syrian talks in Geneva has shown. There is always a danger that the rickety bridge between East and West will further weaken.
Ukraine lies geographically between the two sides. Until now, the shadow of old Cold War rivalries over the territory has largely been kept at bay. Diplomats have argued it ought to be possible for Russia and the West to collaborate over Ukraine's future to the benefit of all sides. But as the crisis worsens, that prospect may be swept away.