Philip Stephens

A year ago we were present at the destruction. The march of US and British troops into Iraq did more than divide old allies over how best to confront Saddam Hussein. It marked the final collapse of the geopolitical architecture that had safeguarded the peace for 50 years. Amid the rubble of the postwar order, we now have incoherence and argument. The consequent risks to the west's security far outweigh the immediate threat of another al-Qaeda atrocity.

The old system, of course, was crumbling before George W. Bush decided to go to war with Iraq. The collapse of the Soviet Union in 1989 removed the existential threat that had bound the US and Europe into the transatlantic alliance. The terrorist attacks of September 11 2001 awakened America to both its unique power and its new vulnerability.

We have heard half a dozen other reasons during the past year or two why the old transatlantic relationship was no longer sustainable. For some, it is simply a question of relative power. America is militarily strong, Europe weak. Once attacked, the US was always bound to discard the old constraints on its freedom of action. After all, the multilateralist impulse that had seen America create the common institutions of the postwar order had been as much an act of realpolitik as of Wilsonian idealism.

The Bush administration, the argument continues, never accepted the bargain under which Europe embraced US leadership in return for a say in the way it was exercised. Primacy meant America could make its own choices and opt for the flexibility of ad hoc coalitions over the obligations of fixed alliances.

There were changes too on the European side of the Atlantic. Just as the fall of the Berlin Wall meant that Europe ceased to be the centre of Washington's geopolitical universe, so too Europe felt less dependent on the US defence guarantee. Germany's implacable opposition to the invasion of Iraq would have been unimaginable during the cold war.

These are all part of the explanation. Behind them lies a deeper divide, rooted in history, culture and geography. Europe's central historical experience has been that military victories produce only temporary peace. The European Union encapsulates a visceral conviction that shared sovereignty, multilateral organisations and the rule of law are the essential explanation for the absence of war. As Jean Monnet once put it:"Institutions govern relationships between people. They are the real pillars of civilisation."

Europeans, though, failed from the outset to understand how profound was the psychological shock delivered to the US by September 11 2001. Flanked by two great oceans, America had considered itself immune from significant attack. The demonstration of vulnerability transformed a status quo power into a revolutionary one.

What we are left with is incoherence. The best that can be said of relationships between Washington and some of its erstwhile allies is that a certain public civility has returned to the conduct of diplomacy. Gerhard Schroder has visited the White House, the president has shaken the hand of France's Jacques Chirac.

A more optimistic view would say that circumstance has also obliged the antagonists to modify their views. I was rereading the other day a speech given by Richard Cheney, the US vice-president, in late August 2002. Historians will see Mr Cheney's text, which seethes with contempt for the United Nations, as a vital moment in the transatlantic rupture.

Yet the grim experience of its forces in Iraq has taught the US something of the UN's value. Only after Kofi Annan, the UN secretary-general, conferred his legitimacy on the process could Washington press ahead with plans to return sovereignty to the Iraqis. Mr Bush, if not Mr Cheney, has learned something of the importance of combining military might with legitimacy.

Europe, of course, has its own confusions and divisions. Tony Blair rested his hopes of keeping the US in the international system on getting up close to the president. Mr Chirac preferred traditional balance-of-power resistance. Both failed. Now the terrorist bombing of Madrid and the outcome of the subsequent Spanish election have added to the fog.

We can dismiss the charge by Mr Bush's Republican allies that the decision of the Spanish electorate to overturn the government of Jose Maria Aznar was an act of terrorist appeasement. You can be resolute against al-Qaeda and yet believe that invading Iraq was a terrible mistake. Those in Washington who now attack Spain's exercise of democracy would presumably argue that a victory for John Kerry in November's presidential election would also mark the triumph of Islamist fundamentalism.

Europe, though, does not have a single or convincing narrative as to how the Pax Americana might work. It is one thing to laud multinational institutions, another to say how they can be remade to meet the new strategic realities and threats. To tell America that it must work through alliances is not enough.

There are, of course, plenty of specific ideas around as to how to reinvigorate the transatlantic partnership. Among those under discussion in coming months will be a new mission statement for Nato and a joint commitment to encourage liberal democracy in what is now called the Greater Middle East.

These are worthy endeavours. But to have meaning they require a change of mindset on both sides of the Atlantic to fit them into a wider framework. There is no need to pretend that the postwar order was perfect. Nor should we think that it can, or should, be rebuilt precisely as it was. But the transatlantic relationship will be fixed only when America and Europe begin to talk seriously about the shape of a new bargain that can accommodate both America's power and Europe's fears. Pace Donald Rumsfeld, the sheriff and his posse will not do it.

I have heard it said that we should be patient. The system that emerged after 1945 was not a single, neat construction. It took many years to create. There was improvisation alongside vision, pragmatism stirred in with principle. That is true, in as far as it goes. But Islamist extremism has not shown itself indulgent of delay. Al-Qaeda will exploit the west's disunity at every turn. And where are today's Trumans and Adenauers, Marshalls and Schumans?