In one classic episode of the British comedy Yes Minister , a senior civil servant detailed the four phases of Foreign Office advice during an international crisis:

Nothing is happening. Something is happening, but we don’t know what it is. We know what it is, but there’s nothing we can do about it. Maybe there was something we could have done—but it’s too late now.

This analysis produced the recommended response: all aid short of help.

In Ukraine, Western governments are now shifting from Phase 2 to Phase 3. We certainly know what is happening: the boldest Russian attempt in a quarter-century to reverse the outcome of the Cold War. Russia has already defied norms of behavior in place since 1945—and threatens to do worse if it doesn’t get more of its own way.

Russia’s annexation of Crimea does not compare to the murderous violence that occurred in recent decades in places like Chechnya or the former Yugoslavia. Nor is it the first time Russia has used force to redraw a boundary in its favor: that occurred in Georgia in 2008.

Yet the attack on Ukraine is different from those previous events in deeply ominous ways. Moscow’s military intervention was triggered by an act of self-determination: peaceful protest against Russia’s attempt to dictate Ukraine’s economic future. Those protests were met with deadly violence at the hands of what almost has to be called a Russian colonial government. Escalating protests drove that colonial government out of power. The seizure of Crimea—now followed by military maneuvers on the eastern borders of mainland Ukraine—is punishment for Ukraine’s exercise of independence.

Russia is sending a message intended not only for Ukrainian ears. It’s a threat to all former Soviet nations. As such, it’s a challenge to the United States—and we need to be very clear about what that challenge is, and what it means.

Tell me if you’ve recently heard a pundit or strategist say something like the following:

Russia is a great power. It is entitled to a sphere of influence on its borders. NATO and the European Union pushed Russia too hard while Russia was weak. Russia is stronger now, and so naturally it’s pushing back. We have to understand Russia’s need for friendly governments on its border.

Familiar, right? Now let’s consider why it’s an awful thing to say.

Every great power, of course, wants friendly neighbors. But the surest way to secure friendly neighbors is to be friendly yourself. It didn’t just happen that Germany is bordered by a friendly France to the west and a friendly Poland to the east. Germany has earned that friendship with its constructive policies in the years since World War II. Germany doesn’t need to subvert French and Polish democracy to ensure French and Polish friendship. Nobody can win an election in France or Poland on a platform of hostility to Germany.

If Russia finds itself in a different situation, it’s because of Russia’s own actions. Russia’s neighbors are frightened of Russia because Russia is frightening. Rather than allay those neighbors’ concerns, Moscow tries to manipulate neighboring political systems and install stooge governments. Neighbors a little further away—Poland, for example, or the Baltic republics—have every reason to worry that Russia would do the same to them, if it could.

But it can’t. And that’s because of the security guarantees enjoyed by NATO members. As a result of that guarantee, Europe—from Estonia westward—is a more peaceful place than ever before in its history. Ukraine is not in NATO; the alliance’s leaders decided that was one extension too many, for reasons both good and bad. Among the good was the rationale that we couldn’t fully rely on the Ukrainian government and military to behave like a proper NATO partner. Ukraine’s officials were too corrupt and easily swayed by Russia; its population’s loyalties too uncertain; and its military capabilities too inadequate. Among the bad were the kinds of arguments summarized in the italicized paragraph above.

The events of the past two months have upended that calculus. A more honest and accountable government in Kiev may follow Viktor Yanukovych’s ousted regime, though reform in Ukraine is no sure thing. We owe this opportunity to an ironic benefit of Russia’s attack on Ukraine: a surge of nationalism. During my recent visit to the country, I met many Russian-speaking Ukrainians who regard Vladimir Putin as a tyrant and aggressor. One senior Ukrainian government official estimated that 40,000 Ukrainians had enlisted in the national guard, though others put the figure somewhat lower.

Realistically, though, Ukraine cannot successfully resist Russia on its own. It needs help, and the West should provide it. “I really think you are more afraid of Russia than we are,” said the same senior official who told me about the enlistments. NATO’s power vastly exceeds Russia’s, and Barack Obama is right to call Russia merely a “ regional power .” Yet when it comes time to make policy, his administration seems to lose sight of the president’s insight.

The Western world’s immediate goal should be to deter further armed aggression by Russia against Ukraine. Ukrainian forces need arms and training, and Ukrainian police may need support even more than the army; it shouldn’t be so easy for bogus Russian “tourists” to cross the border. Western governments must expand their presence in the parts of Ukraine under greatest threat with both consular services and military observers. The more American, British, French, and German bodies stand in the line of fire, the less likely Russia is to shoot.

The next step is to reassure NATO countries in Russia’s neighborhood that the United States can and will defend them. To mollify Moscow, the alliance has not built much of a physical presence in Poland and the Baltic republics. The invasion of Crimea vitiates those promises. It’s time for NATO troops to deploy in the member countries most likely to experience Russian aggression; an occasional F-16 fly-by is laughably insufficient.

It’s also possible—in fact, probable—that Russia will move more cautiously going forward, reverting to its more familiar playbook of bribery, propaganda, energy blackmail, and trade harassment. (Russia has banned Ukrainian confectionary on purported health grounds. I ate some, and they’re fine—excellent in fact—but the loss of Russian sales has hurt one of Ukraine’s few competitive export industries.)

Ukraine will need a lot of economic assistance, and it will have to accept considerable oversight to ensure that the aid is used properly. Tightening anti-corruption practices and laws in Western Europe would help, too. It’s not just Ukrainian politicians who have been plied with Russian money—these funds have flowed through Germany, Italy, and, above all, Britain. Amid Russia’s fierce media war against Ukraine, private Western foundations should support Ukraine’s fledgling independent media. The redirection of George Soros’s philanthropy away from building open societies in Eastern Europe to drug legalization in the United States has done damage to democracy on both sides of the Atlantic.

As a more effective and accountable government takes shape in Ukraine, it will become time to renew its application for NATO membership. This time, the answer should be ‘yes.’

In the long term, the best hope for Europe—and, indeed for Russia itself—is to reduce European dependence on Russian oil and gas. Liquid natural gas from North America can replace pipeline gas from Russia. Carbon taxes—as opposed to goofy carbon-trading schemes—can reduce energy use and enhance the competitiveness of alternative sources of supply. The army Putin uses to bully Europe is an army paid for by European gas consumers. They have it in their power to deprive Putin of his force by denying him their trade.