After an investigation of nearly two months, the Republic of Korea (ROK) has concluded that North Korea torpedoed the Cheonan, a corvette that sank in the Yellow Sea in late March. Today, Seoul is going to the United Nations Security Council.

South Korea must respond to the attack. But no strategy is free of danger. And the ROK’s military alliance with America makes it more difficult for both nations to act in their respective interests.

The so-called Democratic People’s Republic of Korea (DPRK) has been a malign international actor since its formation six decades ago. Kim Il-sung initiated full-scale war in 1950; over the years the regime has engaged in a variety of military and terrorist attacks on both South Korean and American targets.

However, since the downing of a ROK airliner in 1987, Pyongyang has been on better behavior. Brinkmanship has remained the North’s chief negotiating tactic, but the DPRK has avoided committing any blatant acts of war.

Why sink a South Korean ship? It could be an unauthorized military action intended to prevent resumption of negotiations over Pyongyang’s nuclear program. It could be an attempt by Kim Jong-il to demonstrate that North Korea can strike with impunity. It could be a concession by him to the military as Kim attempts to install his young son as his successor. In any case, the attack poses a significant challenge to South Korea. But not to America.

It should be obvious that there is little the DPRK can do to harm the United States. The North lost any significant relevance to American security with the end of the Cold War. Without a link to a potentially aggressive Soviet Union (and, to a lesser extent, a virulently revolutionary China), Pyongyang became an irrelevant backwater.

Even the North’s nuclear program poses no direct threat to the United States. Nothing suggests that Kim is suicidal: he wants his virgins today, not in the afterlife. So he would never strike at America, risking retaliatory annihilation. The prospect of proliferation is worrisome, but again, Kim likely understands the enormous risks he would take selling materials to non-state actors that might target the United States.

Washington is stuck in the center of Korean affairs today only because of the U.S.-ROK alliance, which provides a security guarantee to South Korea with no corresponding benefit to America. Without the alliance, there would be no U.S. troops on the Korean peninsula, within range of North Korean attack, and no American promise to intervene in any war that might result from a provocation by Pyongyang or retaliation by the South.

The sinking of the Cheonan was an outrage, but it was an outrage against the ROK. It should not be an issue of great concern to America, which normally would offer diplomatic backing but not military support to a democratic friend.

Yet American analysts have been producing articles and studies carrying such titles as “America Must Show Resolve over North Korea” and “U.S. Must Respond Firmly to North Korean Naval Attack.”

The question is: why? No American forces were attacked. None are likely to be targeted. The U.S. military already is very busy, especially in Afghanistan. There’s no reason for Washington to risk war over an assault on another state, especially one well able to defend itself.

Were the ROK still a helpless economic wreck, one could concoct an argument for American aid. But the South vastly outranges the DPRK on every measure of national power. The ongoing debate about whether Seoul is ready to take over operational control (“OPCON”) of its own forces along with any U.S. troops during a war is symptomatic of the extreme dependency in which South Korea finds itself. For the ROK to cower fearfully before Pyongyang is roughly the equivalent of the U.S. running to Brussels to request European troops to deter a Mexican attack.

At least the alliance provides an obvious benefit to Seoul: a source of military reinforcement from the global superpower. Still, the South finds its decision-making, even on the question of its national survival, affected and directed by American policy makers half a world away. Virtually every American, from think-tank analyst to Obama administration staffer, has called on South Korea to exercise “restraint.” They say the ROK’s response should be “measured.” They urge Seoul to be “cautious.” And so on.

That makes sense from America’s standpoint. Indeed, the Obama administration has reason to be making much stronger representations privately. It would be folly for the United States to get into a war over the sinking of the Cheonan.

It doesn’t matter that the act was criminal; it doesn’t matter that the deaths have greatly pained South Koreans; it doesn’t matter that Seoul might calculate the costs and benefits of a tough response differently.

Washington’s top priority is avoiding another war, one that likely would be costly, brutal, and bloody — and of no conceivable benefit to America. Obviously, South Koreans have an even greater incentive to avoid war, since their nation would be the principal battleground. However, they might decide that to exhibit weakness in the face of the North’s provocation would make the chance of war even greater in the future. If Pyongyang believes that it can sink a South Korean ship without consequence, what might the Kim regime do next?

Yet Seoul finds its future being decided at least in part in Washington, where America’s, not South Korea’s, interests understandably are treated as paramount. The devastated land that emerged from the Korean War had no choice but to place its security in America’s hands. But the ROK today? In the short-term the U.S. and South Korea are tied together militarily. Their responses to the sinking of the Cheonan will reflect that relationship.

However, both sides should use this crisis to rethink an alliance that has outgrown its original security justification. There is much on which both nations should work together in the future, including military operations where both countries have interests at stake. Such cooperation is not advanced by today’s antiquated alliance.

Neither the ROK nor the United States is well-served by a relationship where South Korea’s fate is decided in Washington. Especially more than a half century after the end of the Korean War and two decades after the end of the Cold War. It’s time to turn South Korea’s defense over to the South Korean people.