The Obama administration is debating a declaration of no first use of nuclear weapons. Some Asia specialists fear the resulting impact on North Korea. But dealing with Pyongyang is a reason for Washington to encourage its ally South Korea to go nuclear.

Washington has possessed nuclear weapons for more than 70 years. No one doubts that the United States would use nukes in its own defense.

However, since then, Washington has extended a so‐​called “nuclear umbrella” over many of its non‐​nuclear allies. For instance, the United States long has threatened to use nuclear weapons in its NATO allies’ defense, though the precise circumstances under which the United States would act were not clear.

Northeast Asia is the region where nuclear threats seem greatest. Japan and South Korea are thought to be snuggled beneath America’s nuclear umbrella, which has discouraged both from acquiring their own weapons.

The “umbrella” obviously is defensive, that is, to protect American allies against the first use of nukes. However, Washington also could—and, it appears, would, if necessary, whatever that might mean—use nuclear weapons first to stop a conventional attack. Russia and China aren’t likely to attack the Republic of Korea or Japan. More plausible is a North Korean invasion of the ROK.

Extended nuclear deterrence always has been risky for the United States. It means being willing to fight a nuclear war on behalf of others. Americans would risk Washington, D.C. and Los Angeles to, say, defend Berlin and Tokyo.

At least bilateral deterrence among great powers tends to be reasonably stable. Dealing with North Korea is potentially more dangerous.

Yet the DPRK eventually may gain the ability to strike the U.S. by developing long‐​range missiles as well as nuclear weapons. The North isn’t likely to attack first, but it still could lay waste to a major American city–which would be a bad deal indeed.

Yet advocates of extended deterrence are criticizing proposals for an American pledge of no first use of nuclear weapons.

The problem is fundamental: It is one thing for Washington to use nuclear weapons, including preemptively, to protect America. It is quite different to do so for allies.

As I point out in National Interest: “Alliances are a means, not an end, that is, a mechanism to help defend the U.S. A North Korean attack on the ROK would be awful, a humanitarian tragedy. But American security would not be directly threatened. Certainly there is no threat warranting the risk of nuclear retaliation on the U.S.”

Of course, those being defended have configured their security policy and force structure in response. But future policy should not be held captive to the past.

Washington’s chief responsibility should be America’s security. Backers of the status quo act like there is no alternative to leaving the ROK (and Japan, which faces a real, though less direct, threat from the DPRK) vulnerable to attack.

However, Seoul is well able to deter and defeat the North. The ROK possesses around 40 times the GDP and twice the population of North Korea, as well as a vast technological lead and an extensive international support network. Japan, which long possessed the world’s second largest economy, also could do far more.

The South is capable of developing nuclear weapons. Indeed, polls show public support for such an option today. Opposition to nuclear weapons is stronger in Japan, but an ROK weapon would put enormous pressure on Tokyo to conform.

Obviously, there are plenty of good reasons to oppose proliferation, even among friends. However, the current system is entangling Washington in the middle of other nations’ potential conflicts. The result is to make America less secure.

Dealing with nuclear weapons is never easy. Washington’s best alternative may be to withdraw from Northeast Asia’s nuclear imbroglio. Then America’s allies could engage in containment and deterrence, just as America did for them for so many years.