Never before, in its 65-year history, has the North Atlantic Treaty Organization faced a threat so close to the one that provoked its initial creation: The prospect of Moscow marching westward into Europe.

And never before have we been made so acutely aware of the alliance's irrelevance to the modern version of that threat.

In the days immediately before this week's NATO summit in Wales, the fields of eastern Ukraine witnessed a spectre not seen since the alliance was created in 1949: Masses of heavily armed pro-Russian irregulars, and what impartial witnesses say were regular Russian troops, shelling and bombarding their way into what one seasoned reporter called a "catastrophic defeat" of the Ukrainian military, leading to humiliating ceasefire terms that resemble nothing more than a Russian occupation of previously sovereign territory.

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On one hand, this military insult was an event that returned NATO to something resembling its original purpose after decades bogged down in the Balkans, in Afghanistan and in North Africa. Some of the alliance's more gung-ho leaders tried to portray this incursion as giving NATO a new sense of purpose: "'Do we need NATO?' was a real debate for a number of years. Putin has ended that debate," Malcolm Rifkind, the chairman of Britain's parliamentary defence committee, said on Wednesday. "We have experienced for the first time since 1945 the annexation of one part of a European country by another by military means."

But, at the same time, it was an event that showed the world how painfully ill-suited this 1940s military alliance is to responding to the very non-traditional military threats facing eastern Europe and the Middle East.

The set of announcements released at the conference's conclusion on Friday were intended to show resolve and unity in the face of an international image of a declining, fragmented Western military. But in many ways they revealed a deeper weakness in the basic organization of NATO and a more profound schism among its members.

The two key planks are the announcement of a rapid-response force and a "readiness action plan" designed to respond to threats with decisive force within "2 to 5 days," and a more or less permanent positioning of NATO troops and weapons in the alliance's Eastern European member states as a supposed firewall against Russia.

The rapid-response force, while something that NATO has been working on and discussing for years, represents nothing either decisive or new. It will take years to organize and implement. And rapid response capability is not something that is currently lacking: As the very quick NATO-organized air-support operation to back Libya's rebels in 2011 showed, there is no lack of quick-response capability in the alliance's military forces.

Should Vladimir Putin's military incursion into Ukraine require a Western military response – a genuine future possibility, but one that would be attempted only after a range of more effective and realistic responses have been played out – there is nothing preventing rapid and crippling air strikes beyond the quite reasonable fear of unleashing a larger war.

If quick response is unnecessary, NATO's other big gesture, the establishment of more or less permanent "forward operating bases" and supply hubs across the alliance's eastern flank, is purely symbolic.

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That gesture speaks to the basic dissonance within NATO's current membership. The organization has, for the past decade, been divided into three very different world views.

The first is that of the United States (and its English-speaking allies), which is capable of meeting any military challenge unilaterally, but which has long relied on the alliance to provide broader international consensus around military responses.

The second are the countries of continental Europe, many of which have large but ineffective militaries designed for ground wars and ill-suited to modern threats; they're also dependent on Russian gas and have been reluctant to back heavy sanctions and military postures.

And the third are the eastern European states – seven former Warsaw Pact countries that were added to NATO's membership in 2004. This added another world-view to the alliance: Many of these countries' leaders view Russia through an old-school Cold War lens: That is, they see the threat being one of thousands of tanks charging across the steppe in a ground-war retaking of territory; therefore, they see the best defence as being an equally old-school permanent basing of missiles and troops along the Russian frontier.

This view, and the demand for Cold War-era bases, has long infuriated military leaders in London, Washington and some Western European capitals and created tension at previous NATO summits. But Mr. Putin's aggression has now created a political counterweight in the East that has forced them to give into this demand.

The problem is that Mr. Putin's approach is is not to engage in a Cold War-style land invasion (though it certainly looked like one in Donetsk last week); rather, it is to stir up rebellion, ambiguity and humanitarian crises in regions he believes can be manipulated; it appears that his end game is not to establish a new Soviet-style empire but rather to destabilize the potentially pro-European countries around the Russian border.

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That may change – and if it did, there would be no shortage of Western military response, with or without permanent "forward operating bases" – but the consensus within NATO countries is that Mr. Putin poses a distinctly 21st-century, unconventional threat. It is not a simple matter of dropping bombs on Moscow, or lining missiles along the Russian border.

The member countries of NATO are perfectly capable of meeting that threat, whatever form it eventually takes, with economic, diplomatic and military tools. The problem is that NATO itself is still organized around a form of threat that no longer exists, and its effort to "show resolve" has only made that basic anachronism all the more visible.