Created as a bulwark against Soviet expansion, NATO is facing an identity crisis as its members grapple with just how much its long and often-unpopular mission in Afghanistan and its new air campaign in Libya size up as national interests _ or not _ when many countries' budgets are under strain.
In an unusually blunt parting speech Friday, outgoing U.S. Secretary of Defense Robert Gates called on the Atlantic allies of the U.S. to pay and do more to overcome the alliance's military shortcomings _ raising the question: What is NATO today, and what does it need to be?
The allies will be doing some soul-searching in the coming months, with Osama bin Laden dead, many European state coffers squeezed by high debt and slow economic growth, the U.S. drawdown in Afghanistan about to start and tough questions about how long its air campaign over Libya could last.
The alliance has grappled with diverging internal views over whether NATO should be an instrument of "hard" combat missions _ generally the U.S. view _ or the preference among some in Europe for "soft" power, like "humanitarian, development, peacekeeping, and talking tasks," as Gates put it.
Ever since the Berlin Wall fell, NATO's raison d'etre has been questioned. Now, with its hands in two military big campaigns in Afghanistan and Libya, the doubts about the alliance's future have hit a new crescendo.
Gates pointed to the "real possibility of collective military irrelevance" and called on members to look at new ways of raising combat capabilities in procurement, training, logistics and sustainment.
Michael Clarke, a NATO watcher and director of the Royal United Services Institute in Britain, said the U.S. still needs NATO as a political conduit to Europe _ but admitted the alliance is struggling militarily.
"There's no doubt that militarily, NATO is approaching something of a crossroads _ it's been approaching this crossroads for some time," he said. Gates, he said, expressed publicly what was long said private: "that NATO's capabilities risk falling below a threshold where they can be effective."
Founded in 1949, NATO was aimed to counter the Red Menace of Stalin's Soviet Union. While that threat is long gone, Gates and others say some of the alliance's 28 member states _ all European except for Canada and the U.S. _ remain too comfortable under Washington's security umbrella.
Gates said the U.S. share of NATO defense spending is now more than 75 percent, and just four other members _ Britain, France, Greece and Albania _ spend more than the agreed 2 percent of economic output on defense.
The former Soviet specialist all but thumped his shoe on the table at Friday's NATO meeting in Brussels, saying its future appeared "dim if not dismal" because of Europe's alleged penny-pitching and aversion to combat.
As U.S. military expenditures rose _ notably under President George W. Bush _ its share of NATO defense spending swelled. Gates cited an estimate that Europe's defense spending fell 15 percent since 2001.
Jan Oberg, a director of the Transnational Foundation, a think tank in Sweden, said the strains are of Washington's own making: by devoting too much money to defense _ or roughly 45 percent of the total $1.7 trillion spent worldwide each year.
"If the secretary of defense of that country tells the rest of the alliance that they are paying too little, the objective truth is that it's a perverse level that the United States is on, and it can forget about ever having the European countries invest as much _ because we're not having any military troubles within Europe," he said.
NATO has come a long way from a high-water mark at the end of the Cold War, when Europe was its focus and it succeeded in staring down the Warsaw Pact, and the Soviet Union and allied Communist regimes collapsed.
After the turn of the new century and the Sept. 11 attacks, the U.S., as a geopolitical power, saw its key security threats migrate east and south _ mainly the Middle East and Central Asia. Europeans tagged along eventually in Afghanistan, often begrudgingly, under the NATO banner.
Washington then eased back from Europe, prodding the continent to shoulder more of its own defense while Washington focused on Iraq and Afghanistan.
U.S. and European security interests have been diverging for years. Gates reiterated concern about a "two-tiered alliance" _ one built on military might, and another devoted to more political and diplomatic tasks.
Clarke said NATO's policy is today determined through talks among its biggest players _ Britain, France, Germany and the U.S. _ and smaller countries can choose to follow or not.
"What we've got now militarily is an ad-hoc NATO, which is that different combinations of the big three or the big four can either make things happen or not," he said.
After the Cold War, NATO successfully expanded to eastern Europe _ with no shortage of grousing by Russia as former Soviet states fell into the Atlantic alliance. Georgia, which once hoped to join NATO, saw its aspirations evaporate with its ill-fated 2008 war Russia _ putting any other NATO move eastward, such as to Ukraine, on ice.
Washington's pitch for such far-afield ventures has been that Europe too faces the threat of radical Islamic terrorism. But it has been an increasingly tough sell, especially in an era of austerity when governments in Europe have to choose between funds for the state pension system or a fleet of F-18s.
Even in countries like France, which fancies its universal values and considers itself a relatively strong military power with postcolonial interests around the world, public opinion remains sour over the Afghanistan mission.
The pressure in Europe against the Afghanistan mission could build as President Barack Obama prepares to lay out a timetable for the start to a U.S. withdrawal of forces in a process that's expected to take until 2014.
There's as much if not more reticence in Germany, which despite its opposition to the Libya campaign remains a key player in NATO by its sheer economic wherewithal _ and despite its postwar aversion to military ventures abroad.
Smaller states like Belgium _ one of the underperforming budget contributors to NATO's defense despite its role in Libya _ want to help Brussels-based alliance remain relevant because of the economic largesse and other spillover benefits its presence confers, Clarke said.
Nordic countries, he said, harbor simmering concerns about Russia _ which helps to explain Norway's and Denmark's participation to help shore up NATO in Libya.
Some analysts say that the Libya campaign is really of France and Britain's making: countries eager to show that Europe can be a military player to stop repression by Moammar Gadhafi's forces, support the Arab Spring, and _ in theory _ leave the U.S. a freer hand on its other missions.
French President Nicolas Sarkozy took political heat at home for allegedly cozying up to now-exiled Tunisian President Zine El Abidine Ben Ali too long. Loath to be caught flat-footed again, France fired the allies' first missile to help repel Gadhafi's forces besieging rebel-held eastern Libya.
France sat out of NATO's military command for decades under a decision by an antagonized President Charles de Gaulle in the mid-1960s. Paris has also long urged continental allies to build a "Europe de la defense" apparatus on the sidelines of _ and allegedly a complement to _ NATO.
Sarkozy finally brought France back into NATO's command structure two years ago.
"The great irony _ huge irony _ is that the French are now fully reintegrated to the NATO alliance just as it's fading away militarily," Clarke said.
Ultimately, many Europeans believe the strong-armed U.S. approach to battling enemies _ using force, not persuasion or other less violent tools _ is wrong-headed and costly, and could spell trouble for NATO, Oberg said.
"If we keep having wars that only a few countries want _ in this case, Libya-France, and other places the United States, and God knows where it will be in the future _ others will ask: Why should we pay for that?"
(This version CORRECTS the name of the NATO watcher to Michael instead of Richard in paragraph 7.)