One of the oddest parties I have ever attended was held at 'Ground Zero', the courtyard in the heart of the Pentagon so named because it was a key target for the Soviet nuclear arsenal in the event that the Cold War suddenly turned hot.

The military top brass, serenaded that afternoon by a country & western band and served ice cold lemonade, was in buoyant mood. Baghdad had fallen. President George W Bush, following his Top Gun touchdown on the aircraft carrier, the USS Abraham Lincoln, had declared that major combat operations in Iraq were over, before the now infamous banner declaring 'Mission Accomplished.'

'Stuff' was happening inside Iraq, as then Defence Secretary Donald Rumsfeld offhandedly acknowledged, after the scenes of mass looting in the capital. But this was very much a celebration, and an unabashed one at that. After all, there was a feeling that in the deserts of Mesopotamia, America's 'Vietnam Syndrome' had finally been put to rest.

Rarely in my BBC career had I delivered a piece to camera that was so at odds with the background mood. Was it not premature, I asked, to hold a victory party when Saddam Hussein had not yet been found, nor a single weapon of mass destruction? Often with television stand-uppers it takes a few tries to get a stumble-free take. With each rendition, I received more disapproving glances. But to us, at least, it seemed a statement of the obvious: the Iraq war was far from over, and the toughest challenges lay ahead.

Ten years on, the Iraq war inventory makes for grim reading. America's military dead number 4487, with an additional 31,965 military personnel wounded in action. The Iraq Body Count database estimates that between 112,000 and 122,000 civilians have been killed in Iraq. The mental cost, both for the Iraqi people and the returning US servicemen and women, is incalculable but profound.

Whatever the changes wrought in Iraq, the financial cost has been colossal. According to the Congressional Research Service, the price tag has been US$802 billion. According to Nobel prize-winning economist Joseph Stiglitz it is closer to US$3 trillion —that would be roughly one-fifth of America's national debt.

Thinking at the Pentagon is now radically different from how it was on that balmy afternoon in 2003, when the sense of military possibility seemed pretty much limitless. As former Defence Secretary Robert Gates memorably put it in early 2011, anyone now advocating a land war in the Middle East or Asia should 'have his head examined.' Nor would anyone propose an open-ended military commitment elsewhere. America cannot afford it, and nor would the American public countenance it. The Pentagon's new strategic guidance document reflects this new political and fiscal reality: 'US forces will no longer be sized to conduct large-scale, prolonged stability operations.' Again, a statement of the new obvious.

A decade on, the 'Vietnam Syndrome' has been superseded by the 'Iraq Syndrome', a hesitancy to embark on new military adventures, a rejection of the doctrine of pre-emption, a return to multilateralism and international cooperation and, as in Iran, a heightened reliance on diplomacy and sanctions. There is a preference, as in Libya, to 'lead from behind', and to fight wars, ideally unmanned, from above. Military planners have come to rely much more heavily on drones and covert action. Counter-insurgency strategies are no longer centred on overwhelming force.

Syria has demonstrated America's strong aversion to enter into conflicts where there is no clear 'exit strategy', even in the face of such stark humanitarian need. A doctrinal approach to foreign policy, favoured by George W Bush and neo-conservatives, has been replaced by pragmatism applied case-by-case.

Far from being a symbol of American military might, as it was in 2003, the Pentagon itself reminds us of the country's relative decline. Over the next decade, it faces budget cuts totaling US$487 billion. Some of its giant aircraft carriers, awaiting refurbishments that the navy can no longer afford, cannot leave port. This includes the Abraham Lincoln.

Doubtless there have been moments of celebration since that 'Ground Zero' hoedown in 2003. The Iraq surge. NATO's involvement in Libya. The killing of Osama bin Laden. But ten years after the Iraq war, the Pentagon is a very different place. A mood of circumspection now prevails.

Image courtesy of Flickr user nkdby.