Doug Saunders is the Globe's International-Affairs Columnist. Follow him on Twitter @DougSaunders.

We're used to thinking of Ukraine as a grey and hazy place of disorder and uncertainty, a country befitting a name that translates to "borderland," just off the edge of the map, between blocs we still insist on describing as "East" and "West."

So when something unambiguous happens in Ukraine, we're forced to start looking clearly into this middle ground and watch our myths shatter under the hard focus of reality.

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This is, above all else, a war of ideas. Along with countless shells and missiles, what Russian President Vladimir Putin has lobbed into Ukraine is a set of ideological challenges to the post-Second World War peace built on progressive pluralism and European cooperation. These challenges, and the urgent need to respond to them, have unseated much of the conventional thinking of our time.

Russia's invasion has not relented despite 298 civilian deaths last week in the downing of Malaysian Airlines Flight 17 by Russia-supplied missiles.

Mr. Putin's assault on the idea of Europe is three-pronged. First, as he told his country's parliament in a March speech justifying the takeover of Crimea, he is waging this war in the name of ethnic nationalism – he is doing so, he said, in order to "defend the interests" of "millions of [ethnic] Russians and Russian-speaking people."

Second, Mr. Putin is doing this in the name of something very similar to imperialism, albeit without the means or ability to really carry it out: An expressed desire to control any territories where Russian is spoken and secession can be engineered (including not just Crimea and eastern Ukraine but also the periphery of Georgia). And third, as a leader who has effectively ended democracy in his own country, he is attacking Ukraine in opposition to the democratic desires expressed freely and fairly by its people.

In other words, Mr. Putin is challenging the three core ideas of the postwar peace. The Brussels-based institutions of modern Europe were built in order to prevent authoritarianism, imperialism and ethnic nationalism from ever again taking root in the continent and leading it to war. It has worked well.

The European response to this new threat, however, has been slow, uncertain and ambiguous. But that shouldn't surprise us, because Putin's challenge has undermined the ideological foundations of prominent groups on both the right and the left, forcing a realignment of ideologies.

To understand the effect Vladimir Putin's actions have had on Europe and the wider world, we should look inside the minds of the three political groups whose ideological assumptions have been unseated by his invasion: the anti-European right; the anti-American left; and the NATO Cold Warriors.

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The anti-Europe right

In the 21 years since the Maastricht Treaty brought the European Union into existence, no member of that 28-country bloc has either become undemocratic or declared war on another member – an astonishing accomplishment in a continent that was mainly authoritarian as recently as the 1980s. What has arisen, though, is a populist politics opposed to the EU itself. The most prominent of these anti-Europe politicians is British Prime Minister David Cameron, who has promised a referendum on EU membership.

The Ukraine crisis has forced these politicians and their backers into a corner. The crisis arose, after all, because a majority of Ukrainians strongly desired EU membership and the higher living standards and free movement that come with it. In 2013, Ukraine's pro-Russian President Viktor Yanukovych, who had been fairly elected in 2010 but had subsequently demolished democratic institutions and jailed opposition leaders, went one step too far when he cancelled a trade pact with the EU, under pressure from Mr. Putin, destroying any chance of a potential pathway to EU membership. This triggered a mass movement to overthrow him and restore the treaty, and led to his ouster by his own parliament.

Suddenly Europe's conservatives have been forced to choose between the EU or Moscow. To the shock of many voters, leaders of successful euro-skeptic parties in Britain, France, the Netherlands, Italy and Austria went with Moscow: Party leaders such as Nigel Farage of the UK Independence Party and Marine Le Pen of France's National Front have voiced outspoken support for Mr. Putin, in good part because he was waging war on the EU, but also because they admire his strongman authoritarianism and opposition to ethnic minorities. Mr. Cameron, visibly appalled by this movement, has abandoned much of his euro-skeptic platform and sided with Brussels: He has repeatedly backed Ukraine's membership bid, to the horror of his more right-wing supporters.

The anti-American left

In the wake of Iraq, Afghanistan, Abu Ghraib, Guantanamo Bay and the NSA spying scandal, many Europeans, especially on the left, abandoned their traditional support for the United States and began to see Washington as a meddling threat to democracy and national sovereignty – many even used the word "imperialist."

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But Ukraine tossed this belief on its head and proved a test for anti-Americans. Most inconveniently, the United States sided strongly with Ukraine's democracy movement, to the point that State Department official Victoria Nuland was recorded, in an apparent Russian phone-bugging in February, discussing which opposition candidate to give Washington's backing and support to (her analysis actually seemed, to Ukrainians, to be very sound). The fact of U.S. backing created an impossible, head-exploding paradox for many Europeans on the left: If Washington was supporting the anti-Putin, pro-Europe movement, then clearly Mr. Putin must be in the right and Ukrainians the victims of Washington's, not Moscow's, meddling.

Nowhere is this line of thinking more prevalent than in Germany. "The Ukrainian conflict with Russia is, for parts of the German population, surprisingly, a conflict with America," writes the German journalist Sebastian Fischer. Polls show that, while most Germans express almost no sympathy or support for Mr. Putin, almost half see the United States, not Russia, as the malevolent force in Ukraine.

German Chancellor Angela Merkel, an instinctually centrist leader who forged her coalition government by hewing close to public opinion, has been slow to impose the sort of sanctions that would be needed to hinder Mr. Putin's ambitions – in part because German corporations are tightly tied to Russia, but also because the German left distrusts Washington more. Members of her foreign ministry have gone further, joining former Social Democrat leader Gerhard Schroeder in embracing Mr. Putin during the crisis. It appears that the Malaysian Airlines catastrophe has provided a reverie-breaking slap for many: During the last week, Germany has become far tougher on Moscow.

The Cold Warriors

Much of this sounds like a return to the days of the Iron Curtain: an expansionist, undemocratic Moscow facing off against a defensive, Washington-focused West in an all-or-nothing standoff. Yet those who believe in this analogy, the Cold Warriors, have been proven equally wrong. NATO's symbolic gestures and its leaders' threats of eastward expansion have been useless at best and counterproductive at worst: They are beside the point.

Those who believe the old East-West divide needs to be reconstituted, that missiles should be lined up along Russia's border, are also missing the point: Russia is not acting out of projected strength, as it did in Soviet times, but out of internal political and economic weakness of a profound degree. This is a failed state on Europe's borders, impoverished and run by a dictatorial clan, lashing out vainly. To respond to its false logic by creating a mirror image of it in the West would be to lend it credibility.

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What needs to be sought is not an amplification of Mr. Putin's myth of a divided continent, but an end to it. A tough economic response is required, along with a generous democratic response that would bring Ukraine into Europe – alongside a refusal to play along with Mr. Putin's attempt to manufacture a civilizational showdown. Ukraine and Russia are both European countries, as much as any other; it is time to put aside our old illusions and help both countries get on the path to peace, prosperity and European values.