Europe's experience has been very different. After 1945 Europe rejected balance-of-power politics and instead embraced reconciliation, multilateral cooperation and integration as the principal means to safeguard peace that followed the world's most devastating conflict. Over time Europe came to see this experience as a model of international behavior for others to follow.

''The transmission of the European miracle to the rest of the world has become Europe's new mission civilisatrice,'' Mr. Kagan writes. Rather than the threat of force and unilateralism, Europe believes conflicts are best resolved through peaceful diplomacy and multilateral engagement. Not war, but inspections is what will secure Iraq's disarmament. ''Thus we arrive at what may be the most important reason for the divergence in views between Europe and the United States,'' he writes. ''America's power and its willingness to exercise that power -- unilaterally if necessary -- constitute a threat to Europe's new sense of mission.''

Mr. Kagan marshals his arguments with care and precision. Contrary to the claims of pundits and politicians, the current crisis in United States-European relations is not caused by President Bush's gratuitous unilateralism, German Chancellor Gerhard Schröder's pacifism, or French President Jacques Chirac's anti-Americanism, though they no doubt play a part. Rather, the crisis is deep, structural and enduring.

Mr. Kagan's thesis has been justly celebrated on both sides of the Atlantic. But it has also come in for some notable criticism. That thesis is, to some extent, a caricature, as he readily admits. There are many Americans (not all of them Democrats) with views indistinguishable from Mr. Kagan's Europeans. And Britain's Tony Blair has made a better case for defeating terrorism and Iraq than has any American.

More problematic is Mr. Kagan's unidimensional conception of power. Though many Europeans may fail to appreciate that military power provides the foundation of security, many Americans fail to appreciate that lasting security requires more than brute force.

It also requires a commitment to uphold common rules and norms, to work out differences short of the use of force, to promote common interests through enduring structures of cooperation, and to enhance the well-being of all people by promoting democracy and human rights and ensuring greater access to open markets.

Mr. Kagan's focus on the military foundation of power tends to ignore these other dimensions of security, all of which are becoming more important at a time of increased globalization. Globalization is a force for both good and ill. It promotes the free flow of goods and ideas across borders, and thus enhances prosperity and undermines repressive regimes. But porous borders can also be exploited by terrorists, organized criminals, narcotics traffickers and money launderers bent on doing harm.

The consequences of globalization are beyond the powers of any one nation to control, even one as powerful as the United States. It requires far-reaching cooperation among many countries to promote globalization's many benefits and defeat its many ills. In the future, much as in the past, the United States and Europe will have to stand at the core of such cooperative efforts. Their challenge, therefore, is to overcome the sources of the differences Mr. Kagan so eloquently describes and forge a new partnership that can deal with the myriad threats and opportunities that define the new era.