Secretary Gates continued his remarkable straight-talk farewell tour when he dared tell Europe that the emperor has no clothes. That was his basic message on Friday when he said that NATO risks irrelevance and a "dismal" future unless Europe begins paying more for its defense.

My initial reaction to NATO when I served alongside our partners in Afghanistan in 2002 was to be impressed with the individual soldiers but underwhelmed by the aggregate contribution of the alliance partners. Despite having invoked Article V for the first time in its history, most NATO allies did not deploy significant material or manpower to the fight: it was clearly the United States' war in the first year. That impression has only deepened since NATO assumed lead responsibility for Afghan security in 2006, nearly losing the war in the process, and undertook a war of choice against Libya in 2011. It has not distinguished itself in either conflict.

What is NATO for? Not for fighting wars. It proved in Kosovo, Afghanistan, and Libya that NATO is not an effective fighting alliance. The wars it fights are fought by committee: or, worse, by bureaucracy. They are clumsy, inefficient, and violate the unity of command, one of the basic principles of war-fighting. Kosovo ended when the Kosovo Liberation Army began to make progress in ground combat and President Clinton appeared to be rethinking his no-ground-forces rule. Afghanistan has only turned around (barely) since the United States effectively re-Americanized the war starting in 2009 (Americans did not make up a majority of international military forces in Afghanistan until then). And Libya is likely to remain stalemated until NATO changes its approach or the United States takes over.

Gates lamented that allies have not spent more on their own defense: buy why should they? The Europeans are not genetically or culturally programmed for pacifism: from the 16^th century onwards each took a turn as the predominant world power, and their empires collectively conquered the globe. Their weak defense today is a simple function of rational choice. The United States subsidizes European free-riding, and the alliance structure is clearly a recipe for moral hazard. Europe has absolutely no reason to spend more on its defense when it can get defense for free from us. They are only doing the rational thing.

But Gates was right when he said that "future U.S. political leaders -- those for whom the Cold War was not the formative experience that it was for me -- may not consider the return on America's investment in NATO worth the cost." That is exactly right. I am a generation younger than Gates, and I have consistently heard (and expressed) these sort of doubts from colleagues and classmates for the last decade.

That is not to say that NATO has no function or that the United States should pull out of the alliance. Far from it. We just need to recognize what NATO really is and what it isn't and then calibrate our expectations appropriately. NATO has evolved (or devolved) from a military alliance into a political institution. It is a sort of institutional expression of the West. It gives voice to common concerns and values. It is the first line of meaningful political (though not military) multilateralism. The possibility of membership in NATO was a powerful incentive for post-communist East European states to reform and implement accountable governance.

More significantly, NATO is a bargain in which the United States commits to Europe's external security in exchange for a European commitment to keep its internal peace. Lord Ismay's famous dictum, that NATO exists "to keep the Russians out, the Americans in, and the Germans down," is still pretty much on target (just replace "Germans" with "secessionists and fascists"). NATO is a tool to balance Russian influence in Eurasia. NATO is emphatically not for global peacekeeping and is not designed for out-of-area operations.

As Russia demonstrated with its 2008 war against Georgia, it is still very much prepared to throw its weight around in its near-abroad. If the United States ever pulled out of NATO and withdrew its troops from Germany and elsewhere, Russia would almost certainly feel emboldened to reassert influence in the Baltics, Eastern Europe, and probably the Middle East, and resurrect an illiberal regional order. NATO helps preclude that scenario. That's a good thing, but don't expect much else.