"The most successful alliance in history," it was called at the end of the Cold War in which NATO, for 40 years, deterred the Red Army from overrunning Berlin or crashing through West Germany to the Channel.

And when that Cold War was over, Sen. Richard Lugar famously said, "Either NATO goes out of area or goes out of business."

In Afghanistan and Libya, NATO went out of area. And given the trend in both conflicts, NATO may soon be going out of business.

NATO faces "collective military irrelevance," said Defense Secretary Robert Gates on his valedictory visit to a stunned Brussels last week:

"The mightiest military alliance in history is only 11 weeks into an operation against a poorly armed regime in a sparsely populated country -- yet many allies are beginning to run short of munitions, requiring the U.S., once more, to make up the difference."

Gates' patience with the Europeans is, understandably, just about exhausted. Two decades after the Soviet Union disintegrated and the Red Army went home, America is still carrying 75 percent of the NATO burden for the defense of Europe.

Only five of 28 members invest in defense the 2 percent of gross domestic product required by NATO rules. Major members like the Netherlands, Spain and Turkey refuse to fly air strikes in Libya. France and Britain have run so low on munitions in a war against a sandbox country on the African coast that they have had to borrow U.S. munitions. Germany and Poland are AWOL.

With an air operations command capable of handling 300 sorties a day, the allies are struggling to put half that many in the air.

Another reason besides European malingering why NATO is in trouble is the fiscal crisis and sea change taking place in the United States.

Gates alluded to it. In America, "the reality is changing. ... Choices are going to be made more on what is in the best interests of the United States."

With GOP conservatives joining congressional Democrats in seeking to cut off funds for the Libyan war, John Boehner has been forced to take the lead in charging the president with violating the War Powers Act. He is demanding Barack Obama come to Congress to get authorization to continue U.S. participation in the Libyan war.

Should the Americans pull out, NATO loses.

The first Republican debate in New Hampshire was astonishing for its anti-interventionist tone. While front-runner Mitt Romney said he would listen to the generals about when it is safe to get out of Afghanistan, he spoke out against any more wars to win independence for nations not vital to the United States.

This is straight out of the Robert Taft tradition that America does not fight other countries' wars or pay other countries' bills.

Michele Bachmann, who emerged as the star of the debate and favorite for the backing of the social conservative and Tea Party right, called Libya a strategic mistake. No vital U.S. interests were imperiled.

That debate was a fire bell in the night for the neoconservatives. The days when Republicans stood up and saluted a commander in chief as soon as he starting bombing a country appear to be over.

With Afghanistan, Iraq, Pakistan and Libya, the GOP appetite for intervention has been sated. Only Sen. Lindsey Graham is hot for air strikes on Syria to bring down President Bashar Assad.

Moreover, there are other reasons, based on painful experience, for the new hesitancy to use U.S. military force. One is blowback, the whiplash recoil that inevitably follows even beneficial U.S. action.

When Obama sent SEAL Team Six on that secret mission to kill Osama bin Laden, we so humiliated the Pakistani army its pro-American commander, Gen. Ashfaq Parvez Kayani, could be ousted and replaced by officers hostile to the United States.

Second, while the U.S. military has shown itself capable of taking down regimes, we have proven less capable of establishing replacement governments that are strong, stable and pro-American. And we have thus far not succeeded at the follow-up business of nation-building, despite the investment of hundreds of billion of dollars.

Third, Americans are fed up with freeloaders, domestic and foreign.

They are fed up with politicians whose constituents pay no federal taxes howling for higher taxes on those who carry the load. Fed up with foreign aid to nations who never get off the dole and regularly vote against us in the U.N. Fed up with allies who spend less than we do on their own defense. Fed up with subsidizing the new international order while nations like China exploit that new order for their own advantage.

"Yankee, go home!" much of the world has been yelping for years. We may be all about to find out what happens when the Yankees do go home, not to return again for a long, long time.