For the past decade, since the end of the Soviet Union, we have been confused about the shape of the world and about the strategic role that Europe can play. But now, as the US begins to clarify its own stance, the options become more apparent. There are four in all.
The first option is to be a willing subaltern to the US. Many say that is what the UK - even the European Union - already is. But it isn't seen that way from the US, and it certainly isn't an overt choice - rather, the European role is more one of unwilling subaltern, who recognises, even on his own continent (Bosnia and Kosovo), that he cannot do much without the US.
Europe is not happy in this role: it talks of increasing its own defence capacity and of uniting its forces. But to become a willing subaltern, Europe would have to acquiesce in US hegemony. What, in any case, can it offer the power that has everything? The US spends more on defence than the next nine states combined; it plans to raise its military budget even higher; and it aims, as a US security scholar wrote recently, to "acquire a capacity to defeat any conceivable type of attack mounted by any imaginable adversary at any point in time - from now to the far distant future . . . a mandate for the pursuit of permanent military supremacy".
The most obvious thing to add to this is intelligence. Europe could concentrate on those parts of the world where its secret services have expertise and networks; at present, only the British do that properly. In the longer term, Europe could supplement US efforts: special forces, paratroopers and marines, flying bomber missions, low-intensity peacekeeping in hostile areas - the more dangerous parts of warfare, in which the British, French and a few others excel. This puts the Europeans into the role almost of mercenaries.
The willing subaltern role would be terribly divisive. Most European countries, led by Germany and France, would not wish to admit that such a role was the best they could do. They would object to putting all their defence eggs into the basket of a foreign power that might one day be indifferent or even hostile. They would be forced to take part in actions with which they might not agree. They would be handing large amounts of sovereignty to a power over which they had no control.
But, it might be said, the unwilling subaltern already does most of these things without the benefits of the increased leverage that a closer alliance might bring. Or rather, the European states other than the UK do it without getting the advantages the UK does. In the war on terror, the British get into the command centre; the other Europeans don't. The British get to share intelligence; the other Europeans don't. Tony Blair knows more about what's happening and what is likely to happen than does any other leader. Condoleezza Rice, the US national security adviser, spends more time with him than with any other leader, apart from her own president.
Britain is the fault line here. Since Suez, it has largely accepted the subaltern's role. Only now is it moving away from it: the agreement with France in 1998 to act as the joint cores of a rapid reaction force roused American anxiety even then, and the anxiety is greater now. If Britain calls it quits on that project - which has progressed little, in any case - it could lead the Italians and the Spanish, say, out of the European defence alliance into the US one.
The opposite of the willing subaltern is the captain of his fate. That option is available in either the united or disunited Europe option. The first involves a European military structure with command and control, multinational forces and joint defence procurement. The European military superpower would then have the size, resources, intelligence and leadership to counterbalance the US military. It would not oppose it: initially at least, it would try to complement it, running joint exercises and preparing to fight common foes.
Such a super-force would probably wish to integrate the Russians and other former Soviet states. It would be a delicate task, because the Polish, Czech and Hungarian forces are under the command of politicians with anti-Russian reflexes and memories of Soviet intervention. But there is a good argument to be made that the integration would smooth away old enmities, and make friends and colleagues of traditional foes: imagine a division composed of French, German, Polish and Russian regiments.
Sooner or later, however, the European force would find itself in awkward corners. Suppose America wanted to intervene in Iran. If Europe's leaders disagreed with this course - as they now do because, unlike the current view in the US, they believe there is merit in engaging Iranian moderates - they might want to deny America the use of bases. Iran and Europe would drift into alliance; the outrage in US policy circles would make America and Europe drift apart.
What of the disunited Europe option? This would involve the maintenance of national defence postures that would go every which way - though not, one would assume, against each other. The larger, nuclear-armed states (Britain and France) would presumably keep the remnants of a global role and would intervene to protect their interests or citizens, or perhaps for humanitarian reasons. The smaller states would remain as now - largely decorative, though sometimes part of an international project. This option would leave Europe painfully conscious of the gulf between each individual force and that of the US. And it could only watch as the Chinese built up their power (some analysts believe the real Chinese defence expenditure is double the official level), as the Russians recovered their strength, and as countries such as India extended their nuclear capabilities.
The fourth and best option - best from the point of view of amour-propre and avoidance of conflict - would be to take up the position of the comrade-general. He would be in charge of a force strategically committed to the US, as US forces would be strategically committed to Europe. In other words, it would be a new kind of Nato - except Europe would have the capability to do many, if not all, of the tasks that the US military currently does.
This would be awkward at first. The US would have to end a 60-year-old strategy: which is to take care of the security concerns of the Europeans, Japanese and others so well that none sees the need to develop independent forces with global reach. The US would be suspicious of European motives. Why should Europeans want to do what their American friends are already doing, fully and generously? But one could envisage an understanding. A European force with real clout could have intervened in former Yugoslavia more quickly and to greater effect. The US could have agreed to assist with materiel and even some troops - but the Europeans would have had the capacity to do it themselves, in an area more important to them than to the Americans.
The agreements would avoid conflict over issues on which there were US-European differences - as in the Iran case. Both sides would have automatic agreement to use each other's bases; any potential adversary would be unable to divide and rule, and would have to factor the US-European alliance into any hostile plans. The agreement would be based no longer on common opposition to the communist bloc, as it was in the days of Nato, but on the preservation of each other's freedom. Intervention in third countries where people were under attack from their own government, or where government had crumbled, would be part of the mission - with a division of labour according to historic areas of interest. Both sides would do the job of global policing.
The great challenges - drawing Russia into a "western" alliance, coping with new superpowers in China and India, assisting African and other poor semi-states in the struggle to provide a decent life for their people - would be agreed and shared ventures. At present, they are overwhelmingly the province of the US, and the consequences are malign. First, they overload the US: it cannot administer, police, placate and mediate a complex world on its own. Second, they infantilise Europe, or consign it to a role of cleaning up after the serious work has been done. Third, they give the US no challenge to its own conceptions - challenges that it will need if it is not to rely on pressure and threats.
None of these options is wholly pleasant. But they will have to be faced. Europe risks irrelevance if it does not make the consequences of America's unprecedented military superiority clear to its own citizens, and seek their consent for a clear strategy of living with it, beside it or under it.