The United States has defended South Korea for 50 years. But newly elected President Roh Moo-hyun suggests that his nation might “mediate” in any war between America and the North.

Whatever value the U.S.-ROK alliance once had has disappeared. The presence of 37,000 troops in South Korea is a Cold War artifact, resulting from the post-World War II division of the peninsula and subsequent Chinese and Soviet support for North Korean aggression. Today the Cold War is over and China and Russia are friendlier with Seoul than Pyongyang. Moreover, the South has raced ahead of the North, enjoying 40 times the GDP, twice the population, and a vast technological edge. The DPRK’s military is large, but decrepit. To the extent that the ROK’s military lags behind that of its northern antagonist, it is a matter of choice, not necessity.

Although no U.S. forces are needed to guard against the bankrupt North, they are ubiquitous, with some based in downtown Seoul. Thus occur purposeless violent altercations and tragic traffic deaths.

After the acquittal in military court of two soldiers charged in the accidental deaths of two children, demonstrations erupted. Americans have been barred from restaurants, jeered, and in a few cases, physically attacked.

President-elect Roh has called for a more “equal” relationship and promised not to “kowtow” to Washington. Even the United States seems prepared to change the status of agreements governing the treatment of American servicemen.

But the relationship between the two countries will never be equal so long as South Korea is dependent on Washington for its defense. And so long as America protects the ROK, it will rightly demand special treatment for its soldiers. Put bluntly, there is a price to be paid for being a protectorate.

That is even more evident when it comes to policymaking on the peninsula, including toward North Korea, which Washington continues to dominate. A misstep toward Pyongyang would be bothersome for the United States; it would be catastrophic for the South. Yet, former President Bill Clinton relates: He prepared military options for use against the North a decade ago, with nary a nod to the South Koreans (and Japanese). President George W. Bush apparently rejected military coercion only because Korean President Kim Dae Jung personally related the horrors of the Korean War.

That is a thin reed for Seoul to rely upon in avoiding a new Korean War. As Roh recently complained, “We almost went to the brink of war in 1993 with North Korea, and at the time we didn’t even know it.”

Nor can Washington feel comfortable about shifting attitudes in South Korea. The generation grateful for American aid in the Korean War is passing from the scene; younger people, who will make up an increasing share of the electorate, think more of U.S. support for various military regimes and the indignities (and tragedies) of a foreign military presence.

Moreover, Seoul’s increasing assertiveness in developing its own policy toward the North is likely to increase. The best strategy for handling the DPRK is not obvious, but it is not surprising that policymakers in Seoul, within easy reach of North Korean artillery and Scud missiles, have a different perspective than those in Washington.

The most momentous issue involving the Korean peninsula today is Pyongyang’s continuing pursuit of nuclear weapons. Halting its program is an important goal, but is not advanced by America’s existing troop presence.

Absent a U.S. plan to invade the North — something that seems unlikely even in the Bush administration — the U.S. forces perform no useful role. To the contrary, they are nuclear hostages if the North marries an effective atomic bomb to a means of delivery, which it may have already done.

A better strategy toward the North will come through a coordinated response from all of its neighbors, particularly China, Japan and Russia. None want war on the peninsula; none want a nuclear North Korea; all possess some degree of leverage over Pyongyang.

The basic message needs to be: Significant diplomatic and economic rewards are possible, but only for positive, verifiable disarmament. More aggressive behavior, in contrast, will encourage both Japan and South Korea to respond in kind, which would not be in Pyongyang’s interest.

In contrast, Washington should move to the background, downplaying the crisis. This would sharply reduce the value of the DPRK’s nuclear card.

Alliances exist to serve a purpose. Yet in Korea, the means has become an end. America’s military presence is no longer necessary to protect the South; it plays no role in constraining China or, even less plausibly, Japan.

The relationship’s diminishing utility is most evident in the South. Seoul bears the cost of hosting foreign troops, runs the risk of having its security controlled by a self-centered great power and craves the respect due a country moving toward the first rank of nations.

Even if the countries avoid a crisis today, they will only delay the inevitable. America’s security guarantee has lost its raison d’etre. It’s time for an amicable divorce rather than a much more bitter parting in the near future.