The growing tensions between South Korea and the United States have startled and angered many Americans.

It was not long ago that the alliance with South Korea seemed to be one of this country’s most stable relationships. Now, scarcely a day passes in Seoul and other cities without massive street demonstrations against the U.S. military presence.

The growing anti‐​Americanism has even had a dramatic impact on South Korean politics. Roh Moo‐​Hyun, the country’s president‐​elect, owes his position largely to his decision during the final weeks of the campaign to portray his conservative opponent as a stooge of Washington and to emphasize his own willingness to stand up to the United States.

But South Korea is hardly the only U.S. ally to experience a surge in anti‐​American sentiment.

The Bush administration has come under withering fire from officials and opinion leaders in Japan and the NATO countries as well regarding an assortment of issues. Across the world, the United States is encountering a pervasive phenomenon of ungrateful allies.

Administration officials tend to minimize these developments and attribute them to isolated, minor causes.

For example, U.S. leaders argue that the recent tensions in South Korea occurred because of an unfortunate incident in which an armored personnel carrier killed two Korean school girls in a traffic accident. The soldiers involved in the incident were acquitted by a U.S. military court, sparking a ferocious reaction among the South Korean people.

The real causes run much deeper, however. Increasingly, the turbulence in America’s alliances result from fundamental differences in perspectives and interests between the United States and its allies. That means that intra‐​alliance disagreements are likely to grow more intense and acrimonious in the coming years.

South Korea is a case in point. The growing anger toward the United States is not merely the product of a tragic traffic accident or even the long‐​standing South Korean resentment that U.S. military personnel stationed in their country are not generally under the jurisdiction of South Korean law.

Instead, the most potent source of discontent concerns policy toward communist North Korea. Many South Koreans believe that the Bush administration has deliberately sabotaged Seoul’s “sunshine policy” of seeking better relations with the North.

South Koreans also generally favor solving the North Korean nuclear crisis through dialogue and concessions. They know that Washington prefers a more hard‐​line policy, and they fear that such a policy could lead to a military confrontation and perhaps trigger a disastrous war on the Korean peninsula.

Those are serious policy differences, and the resulting anger reflects the frustration of a security‐​dependent nation. South Korea has benefited handsomely from being under the U.S. security umbrella. South Korean military experts concede that the country would probably have to spend an additional $12 billion to $15 billion a year on defense if it had to provide for its own security without U.S. assistance.

South Korea could clearly afford to do so. It has an economy 40 times larger than North Korea’s and a population twice as large. Seoul merely prefers to spend its money on other things.

But the downside of depending on the United States for defense has now become evident. South Korea does not control policy on an issue that is vitally important to the country. Instead, Washington calls the shots and South Koreans realize just how vulnerable they are if the United States chooses a reckless course of action.

Relatively few South Koreans, however, want to take the logical (albeit drastic) step of terminating the alliance and taking control of policy. Instead, they want the best of both worlds. They want to continue to be defended by the United States but only on terms dictated by South Korea. That is an unrealistic expectation.

The NATO allies exhibit a similar bipolar disorder when it comes to policy. The same impotent frustration regarding their dependence on the United States is evident.

Most European governments and publics believe, for example, that U.S. policy toward Iraq is dangerously misguided. They also differ sharply with the United States on such issues as the Israeli‐​Palestinian conflict, the Kyoto Protocol on the Environment, and the International Criminal Court. Like South Korea, the European allies are dismayed when Washington ignores or rebuffs their objections.

But like South Korea, the NATO allies do not want to lose the benefits of being defended by the United States.

If the European countries became responsible for their own defense and the overall stability of their region, they would have to spend significantly more on their anemic militaries and shrink their bloated welfare states.

They would also have to be willing to deal with messy problems such as Balkan quarrels instead of looking to the United States to share much of the burden.

They could — and certainly should — do so. Collectively, the nations of the European Union have an economy larger than that of the United States and a population substantially larger.

Instead of strengthening their militaries and taking on more security responsibilities, however, the Europeans prefer to continue free‐​riding on the U.S. defense commitment even as they complain incessantly about the substance of U.S. policies.

They want the United States to be their superpower protector, but a tethered superpower. That goal is as delusional as the South Korean objective.

It would be better for both the United States and its allies to agree to an amicable strategic divorce.

On issue after issue, our policy preferences — and our underlying national interests — diverge sharply. And that divergence is accelerating. During the Cold War, there were also disagreements. But they were milder and the existence of a dangerous mutual threat, the Soviet Union, prevented those disagreements from rupturing the security ties.

In the 21st century, there is no mutual threat to act as the necessary glue to hold Washington’s alliances together. Sooner or later, a strategic divorce is coming.

The longer the United States waits, the more likely it is that the divorce will be a bitter one.