Mitt Romney surprised — and likely encouraged — many in foreign policy circles during this week's presidential debate when he rejected future Iraq-style wars and insisted "We can't kill our way out of this mess" in the Middle East.

This was one of the purest backflips by a Republican candidate known for his shifting positions, and at odds with the bombast of some of his former hardline positions.

Still, while some of this was likely aimed at those elusive swing voters, many analysts believe this new position reflects not just the reality of war-weary America but what some are calling the "strategic insolvency" of Washington's clout on the world stage

"What [the debate] told us above all is that the American people are in a different place," noted Zbigniew Brzezinski, a global strategist and former national security adviser.

These politicians, he says, "knew they were speaking to a country that doesn't want more military interventions."

Looking at the debate, political analysts focused on the Romney flip-flop, while the foreign policy folks saw something potentially historic, the apparently bipartisan acceptance of these new power realities.

As David Ignatius of the Washington Post put it: "Both candidates are recognizing that there are limits to what America can do, and perhaps more importantly, limits to what the American public is willing to tolerate."

Critical mass

Is the sun setting on U.S. military intervention abroad? Here the USS George Washington cruises off Manila Bay in October 2012. (Bullit Marquez/Associated Press)

The reality facing anyone running for president these days is that Americans are clearly looking inward to their economic woes.

Voters are impatient to end the big, expensive military interventions, such as in Afghanistan, and according to an October survey by the Pew Research centre, fully 63 per cent of Americans want to see the U.S. "less involved" in the Middle East.

Perhaps more important is the deepening realization around Washington that America must now develop a different "grand strategy" for the future, one it can actually afford.

It would be a strategy that fully accepts the fact that the U.S. no longer has the wherewithal — whether militarily, diplomatically or economically — to bear the full weight of global obligations.

An era may be ending.

Over-extended

For a generation, following the end of the Cold War in 1989, the U.S. strategic debate "has been over what form of hegemony to seek, not whether to seek it," says analyst Barry Posen, a prominent political scientists at MIT.

Now, as one hears from an increasing number of military and foreign policy strategists, the next president, even a Republican one, will find that position unsustainable.

Indeed, these days, Pentagon scholars and global economists are debating the ways in which the U.S. must soon start to diminish its overseas commitments rather than extend them.

And while the risk of Big Power over-extension has been debated in the past, what's new is the sense that this feared future has finally arrived.

"The forces undercutting the U.S. strategic posture are reaching critical mass," warns the hottest policy study now being passed around Washington these days.

Titled The Risks of Ignoring Strategic Insolvency, the paper by Michael Mazarr, a highly regarded scholar at the U.S. National War College, says: "The question for the United States now is whether it responds to this emerging reality, or continues doggedly trying to ignore it."

The 5 reasons

For Mazarr, there are five key reasons why the U.S. must reshape its strategy as the world's pre-eminent power.

The first is most obvious. The U.S. simply cannot afford such global primacy given its national debt, which some warn will hit a crushing 100 per cent of GDP within eight years.

To avoid budgetary disaster, hundreds of billions of dollars must inevitably be cut from the military (even if Romney wins) and other foreign policy arms.

Secondly, rising new powers such as China, Brazil, India and Turkey simply won't accept dominant U.S. leadership anymore.

"A fundamental reality of the past two decades or more has been an emerging reaction against U.S. primacy," Mazarr writes, adding that this has, in areas such as the Middle East, even spilled over into resentment of U.S. "social and cultural hegemony."

A third reason is that rising powers are developing such advanced military technology that the U.S. will be unable to "project power" into key regions of the world.

Saving his ammo? Republican presidential contender Mitt Romney acknowledges veterans at a Nevada rally in October 2012. (Charles Dharapak/Associated Press)

China and Russia, for example, are beginning to possess technology such as anti-ship missiles and drones, along with the ability to create so-called cyber-mayhem, that makes military showdowns increasingly hazardous.

Add to this that America's futuristic military systems, like the giant super-carriers, are becoming prohibitively expensive to build and staff (making them almost too valuable to risk losing in combat).

The wars in Iraq and Afghanistan have severely exhausted existing forces to the point where 60 per cent of naval and marine aircraft were not considered "mission ready" last year.

Fourth, Mazarr cites a loss of U.S. credibility abroad after so many national political and economic setbacks at home and abroad.

In an increasingly complex world, where problems generate no broad agreement on solutions, the once dominant U.S. model now seems less reliable even among Western allies, Mazarr suggests.

The fifth reason is that, as mentioned above, there's no broad domestic consensus in the U.S. to back up the use of its military muscle abroad.

Mazarr argues that Washington can still retain a respected leadership role on the world stage, but only by reducing its own obligations abroad and drawing more countries into power-sharing coalitions and alliances.

Canada should probably follow this strategic debate closely for a leaner U.S. will certainly press for much more supportive load-carrying from its allies.

So we probably need to start rethinking our own strategic goals — and limitations — at the same time.

As Mazarr notes, quoting the towering 19th-century Prussian statesman Otto von Bismarck, "the essence of strategy is the ability to hear the hoof prints of history."

And today they are thundering in the background.