IN 1997, when the world was a gentler place, NATO and Russia came to a far-reaching security agreement. As part of this, the Kremlin accepted the idea that several countries from the former Warsaw Pact would become full members of the alliance; in return, NATO agreed not to mass lots of troops, equipment and nuclear missiles on Russia’s border. Now Russia’s president, Vladimir Putin, has annexed Crimea and is threatening eastern Ukraine. This is particularly scary for the three Baltic states which became members of NATO in 2004: Estonia and Latvia both have Russian-speaking minorities of the sort Mr Putin “protected” in Crimea, while Lithuania stands between mother Russia and its Kaliningrad exclave. All three have been a target for Russian mischief, from cyberattacks to mock invasions. The Balts worry that the West will not protect them (see article). It is not hard to see why. Mr Putin has an inkling that NATO’s newer members are second-class citizens. There is some truth to this. For a long time before Russia’s annexation of Crimea, the alliance’s western powers pooh-poohed warnings from east of the Oder that Russia still posed a threat. NATO refrained from drawing up contingency plans against a Russian attack on its former vassals or from holding exercises to demonstrate that it knew how to defend the east. Even today, when it does have plans and exercises, only 136 of the 66,217 American troops in Europe are based in the central and eastern parts. Until now, Russian aggression towards the Baltics has been met with words from the West, and little else.

Instead, the West should forcefully reassert NATO’s willingness to defend itself and make it clear that all members of the alliance share its complete protection (see article). In particular, that means other NATO members sending at least a few troops, missiles and aircraft to the Baltics (or to neighbouring Poland), and making clear that bigger forces will follow if there is any continued aggression from Mr Putin.

Why go that far? Plenty of people in the West would prefer to “wait and see”. The Balts have the promise of protection, they point out, so there is only danger in provoking Mr Putin. Wishful thinkers say that having made his point in Crimea, he will probably stop while he is still ahead. Instead of ratcheting up tension, the West should provide “off-ramps” that steer Russia towards détente. Other hard-nosed foreign-policy “realists” argue that Russia has legitimate interests in its near-abroad. It is madness, they say, to pick a fight when Russia and the West have other business to be getting on with—Syria’s civil war, Iran’s nuclear programme and China’s growing power.

Hot foot from the cold war

In fact the opposite is true. The greatest provocation to Mr Putin is to fail to stand up to him, and the least costly time to resist him is now. Emboldened, Mr Putin could test NATO’s resolve by changing the facts on the ground (grabbing a slice of Russian-speaking Latvia, say, or creating a corridor through Lithuania to Kaliningrad) and daring the alliance to risk nuclear war. More likely he would try destabilisation—the sabotage of Baltic railways; the killing of Russians by agents provocateurs; strikes, protests and anonymous economy-wide cyber-attacks. That would make life intolerable for the Balts, without necessarily eliciting a response from the West.

Either way, if the Balts begin to disintegrate, it would leave the West with a much less palatable choice than it has today: NATO would have to walk away from its main premise, that aggression against one is aggression on all, or it would have to respond—and to restore deterrence, NATO’s response would have to be commensurately greater. That in turn would pose the immediate threat of escalation.

Better to take steps today, so that Mr Putin understands he has nothing to gain from stirring up trouble. Barack Obama, visiting the alliance’s headquarters this week, made a start, by reaffirming the principle of mutual protection and saying that some American troops would be shifted eastwards. More is needed. More exercises should take place in eastern Europe. The region’s air and cyber defences need boosting. NATO’s next head, to be appointed in September, should be someone who understands Russia—Jens Stoltenberg, a former Norwegian prime minister, or Radek Sikorski, Poland’s foreign minister. The alliance should work with Sweden and Finland and leave the door open to their membership. And all members should honour their pledge to spend 2% of GDP on defence.

With its difficult mission in Afghanistan drawing to a close, NATO had been looking for a purpose. Mr Putin has given it one. If the leaders of NATO countries can show they understand that, then all of Europe will be safer.