With their decision Tuesday to escalate sanctions against Russia over Ukraine, Europe’s leaders have finally injected a little spine into their diplomatic posture.

The need to respond to Russian President Vladimir Putin’s provocations in Ukraine has been clear for some time, and it’s hard to understand why it has taken Europe so long. At the same time, resolving that crisis – and meeting the broader challenge posed by a vengeful Russia – will require not only the continued unity of the European Union and U.S., but also a willingness to engage Russia.

Among other things, the sanctions worked out in Brussels among the EU’s 28 members ban Russia’s state-owned banks from selling stock or long-term debt on European markets, block shipments of high-tech oil-drilling equipment and impose an embargo on future arms shipments.

These new steps – which the U.S. subsequently complemented – impose significant pain on Russia’s $2 trillion economy and on some European companies. Yet the EU also carved out some glaring exceptions: France gets to proceed with the sale to Russia of the first of two Mistral helicopter carriers, for instance, and Germany doesn’t have to worry about sanctions on Russia’s natural gas, on which it heavily depends.

This aversion to pain illustrates the asymmetry that often underlies sanctions, which countries use only when they don’t care enough to go to war. The EU and NATO may not care enough about Ukraine to take up arms, but the same can’t be said about Putin, who has ratcheted up Russia’s military engagement with the rebels, launching attacks from Russian territory on their behalf. What’s more, his aggression has won him frothy public approval ratings.

Stiffer sanctions are a long-overdue reminder to Russia that aggression can have steep consequences. But they won’t resolve Russia’s deep-seated concerns about its own security. As hard as they may be for some Westerners to fathom, they nonetheless demand awkward, difficult and high-level diplomatic engagement.