Published: July 8 2003 20:14

If one has a hammer, everything looks like a nail. Many in and around the Bush administration think US military preponderance, directly applied, can solve their country's security problems. They are wrong. The efficacy of vast force is smaller than they believe.

What is happening in Iraq is a telling indication of these limits. The US today is turning out to be even weaker than the 19th century European imperialists some Americans wish to emulate. How can that be? Does the US not account for 40 per cent of the world's military spending? Did its armed forces not overthrow Saddam Hussein's regime in a three-week campaign with negligible casualties? Yes, is the answer to these questions. The US possesses a fine hammer. But the challenges it confronts are not all nails.

In two respects at least, US military power is constrained. First, it cannot safely use its conventional preponderance against a nuclear-armed enemy. Second, winning wars does not translate readily into stable peace. Coalition forces in Iraq number over 150,000. Some informed observers believe that the force required to generate the necessary sense of personal security among ordinary Iraqis is closer to 300,000. Given force rotation, almost the entire US army could be absorbed in the task. Providing security in a country that in the 1920s was a tiny portion of an ailing British empire could absorb a huge part of the superpower's military for years.

What sort of overwhelming military power is this? The answer is less than supposed. Smart weapons and technological wizardry cannot deliver tranquillity and order. These require effective forces, street by street, and the co-operation of those they control.

Admittedly, competent planning could have reduced the difficulties the US confronts. As Jessica Tuchman Matthews, president of the Carnegie Endowment, notes, in From Victory to Success: Afterwar Policy in Iraq: "The difference in how seriously the US addressed the war and the postwar can be found in the priority assigned to the exercise of force versus that given to other instruments of power and influence . . Only in the non-military side does the US indulge in goals, means and public commitments that bear no relation to one another."*

The amateurism shown since the end of the campaign is indeed scandalous. But it is made more shocking by the enormity of the task. Just how hard nation-building is can be learned from an analysis by Minxin Pei, also in From Victory to Success. In an analysis of 16 US attempts at nation-building, just four (post-second world war Japan and Germany, Panama in 1989 and Grenada in 1983) were successful. In these four cases alone was democracy maintained for at least 10 years after the end of the occupation. Of the 12 unilateral attempts, 10 failed.

Japan and Germany were ethnically homogeneous and industrially advanced. They also contained highly literate populations with sizeable middle classes. In effect, these were advanced societies that had taken a wrong turning. Iraq is not in the same category. Obstacles include the absence of experience with democracy; atomisation of civil society; the country's ethnic, tribal and religious divisions; the lack of independent institutions; and the role of oil as the source of income for government.

The combination of these long-term obstacles with chaotic initial conditions create a profound dilemma for the occupiers. To engender the security needed to make anything work, their behaviour must be credibly coercive. Yet such coercion undermines the legitimacy of the occupation in the US, the rest of the world and Iraq. There it will turn bystanders into opponents and opponents into rebels.

In the language of economists, an occupation is not "incentive compatible": the behaviour required to make it work is inconsistent with the perceived interests of the occupiers or the occupied. Even to obtain minimal co-operation requires a credible commitment to stay, since those who co-operate must otherwise risk the post-occupation fate of collaborators through the ages. But a democratic US cannot give such a commitment.

These difficulties are far greater today than they were a century or more ago. What happens on the ground is transmitted at once across the globe. Domestic electorates are aware of what occupations cost, in lives and resources. The occupied are not the tradition-bound peasantry of ancient agrarian societies. Modern technology allows them to communicate easily with one another and with the outside world. They are also aware of ideas of self-government, democracy, nationalism and now of an Islamic religious revival. The British Indian empire was a creature of its time. It could not now be repeated.

All government depends on the consent of the governed. The less coercive one wants an occupation to be, the more important such consent becomes. Rightly, the US cannot replicate the tactics of Nazi Germany or the Soviet Union in occupied territories. But a democratic, law-governed occupier is bound to find it far more difficult to secure the consent of the occupied in the 21st century than it was in the 19th.

What, then, are the conclusions? First, the occupier needs to secure its legitimacy among both the occupied and those whose help it is likely to need. Today, such legitimacy can only be achieved through the activities of multilateral institutions.

Second, a unilateral US cannot expect full support from its allies. Most intelligent Europeans want the US to succeed with its occupation, whatever they thought of the war. That does not mean they wish to commit resources and people to support an occupation for whose existence they had no responsibility and over whose direction they have no influence.

Third and most important, the US must understand the limits of its military power. The assumption that its preponderant might makes it simple to rearrange the internal politics of the world is fatuous. This does not mean that the effort should never be made. Sometimes, indeed, it is inescapable. But if the US attempts to achieve its goals through a militarised foreign policy that scorns both the views of its allies and the role of global institutions, it will fail. And that would be a tragedy, not just for the US but for the world.