If Asia, with its dynamism and power struggles, in some ways resembles the Europe of 100 years ago, the Middle East is more reminiscent of the Europe of several centuries before: a patchwork of top-heavy monarchies, internal turbulence, unresolved conflicts, and nationalities that cross and contest boundaries. Europe’s ability to influence the course of this region, too, will be sharply limited.

Political and demographic changes within Europe, as well as the United States, also ensure that the transatlantic alliance will lose prominence. In Europe, the E.U. project still consumes the attention of many, but for others, especially those in southern Europe facing unsustainable fiscal shortfalls, domestic economic turmoil takes precedence. No doubt, Europe’s security challenges are geographically, politically and psychologically less immediate to the population than its economic ones. Mounting financial problems and the imperative to cut deficits are sure to limit what Europeans can do militarily beyond their continent.

Moreover, intimate ties across the Atlantic were forged at a time when American political and economic power was largely in the hands of Northeastern elites, many of whom traced their ancestry to Europe and who were most interested in developments there. Today’s United States — featuring the rise of the South and the West, along with an increasing percentage of Americans who trace their roots to Africa, Latin America or Asia — could hardly be more different. American and European preferences will increasingly diverge as a result.

Finally, the very nature of international relations has also undergone a transformation. Alliances, whether NATO during the Cold War or the U.S.-South Korean partnership now, do best in settings that are highly inflexible and predictable, where foes and friends are easily identified, potential battlefields are obvious, and contingencies can be anticipated.

Almost none of this is true in our current historical moment. Threats are many and diffuse. Relationships seem situational, increasingly dependent on evolving and unpredictable circumstances. Countries can be friends, foes or both, depending on the day of the week — just look at the United States and Pakistan. Alliances tend to require shared assessments and explicit obligations; they are much more difficult to operate when worldviews diverge and commitments are discretionary. But as the conflicts in Iraq, Afghanistan and now Libya all demonstrate, this is precisely the world we inhabit.

For the United States, the conclusions are simple. First, no amount of harping on what European governments are failing to do will push them toward what some in Washington want them to do. They have changed. We have changed. The world has changed.

Second, NATO as a whole will count for much less. Instead, the United States will need to maintain or build bilateral relations with those few countries in Europe willing and able to act in the world, including with military force.

Third, other allies are likely to become more relevant partners in the regions that present the greatest potential challenges. In Asia, this might mean Australia, India, South Korea, Japan and Vietnam, especially if U.S.-China relations were to deteriorate; in the greater Middle East, it could again be India in addition to Turkey, Israel, Saudi Arabia and others.

None of this justifies a call for NATO’s abolition. The alliance still includes members whose forces help police parts of Europe and who could contribute to stability in the Middle East. But it is no less true that the era in which Europe and transatlantic relations dominated U.S. foreign policy is over. The answer for Americans is not to browbeat Europeans for this, but to accept it and adjust to it.

Richard N. Haass is president of the Council on Foreign Relations. The director of policy and planning at the State Department from 2001 to 2003, he is the author of “War of Necessity, War of Choice: A Memoir of Two Iraq Wars.”