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This is a little book about big things. For more than half a century, Sir Michael Howard has represented the most elegant and civilised face of the argument for Western defence. He was never a hawkish Cold Warrior, but always an impenitent advocate of the need for Nato to present a strong shield against the Soviet empire. At the age of 78 in the post-Cold War era, he has now written a superbly crafted essay, explaining why the West would be foolish to assume that permanent peace has come upon us.

It is impossible to predict what form a new military conflict might take, but some time it seems overwhelmingly likely that it will come. "Bourgeois society is boring," he observes drily. "Militant nationalist move-ments or conspiratorial radical ones provide excellent outlets for boredom. In combination, their attraction can prove irresistible."

Europe's shrunken defences today reflect a world in which European governments know that their voters have no appetite for military spending. They maintain armed forces only at the minimum level thought necessary to keep America engaged on the continent.

British forces are increasingly focused upon a capability to intervene in humanitarian causes overseas, where Mr Blair's government can satisfy itself - in a remarkable inversion of history - that this country has no selfish national interest. Sir Michael is sceptical about the merits of such operations, without mentioning Sierra Leone explicitly: "There were many ways in which the West could influence the development of the post-colonial world, but, with very rare exceptions, overt military intervention was not one of them."

To justify the belief that we have achieved a permanent state of world order, we should need to see a world of like-minded states, which is plainly lacking. Howard remains wary of the peril posed by societies which either reject our version of bourgeois capitalism, or fail to achieve it. Capitalism only works, he observes, where stable civil societies exist to support it. When they do not - as in Russia today - capitalism may yet fail, and xenophobia, authoritarianism and nationalism thrive. In many Islamic societies, the flag of triumphant capitalism is seen as a symbol not of liberation, but of alien oppression: "Marx's warning of the tensions created by a global market economy remains valid, even if his prescription for resolving these has not."

Sir Michael warns against expecting too much of international organisations, when the individual state and the people who inhabit it remain the key elements, the only effective mechanisms for decision and action. In the Middle Ages, the Church provided an effective supra-national unifying element between the major European nations. This was replaced from the 17th to the 19th centuries by the noble and educated ?lites. Today, there are only the uncertainties of the bourgeois consensus.

In the "post-heroic age ... the kind of patriotism that enabled the people of Europe to endure two world wars now appears as archaic as the feudal loyalties that it displaced. The national flag is no longer a symbol to evoke awe and respect. At best it is the logo of a firm - Britain plc - whose function is to provide dividends for its shareholders."

Self-interested businesses are unlikely to feel much interest in great but remote issues of global security. The United States is one of the few major nations where old-fashioned patriotism still holds sway, but Sir Michael has reservations here too, about America's ability to use military power effectively, when casualties have become politically repugnant: "People who are not prepared to put their forces in harm's way fight at some disadvantage to those who are."

This essay is a brilliant reflection on the world in which we live, and the potential threats to it. At root, Sir Michael echoes the message of sensible statesmen and soldiers through the ages: you never can tell. Because today we live in ever more parochial social tranquillity, we find it ever harder to imagine any great external threat, or to fund and support the precautions against it. Howard's warning, based on vast wisdom and experience, demands to be read by a generation of European politicians increasingly blinded by trivia.