Extended Deterrence in the U.S.-ROK Alliance
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Interview

Extended Deterrence in the U.S.-ROK Alliance

Interview with Mira Rapp-Hooper
April 28, 2020

Following the failure of the United States and North Korea to reach an agreement on denuclearization at the Hanoi Summit in February 2019, Pyongyang has reverted to a pattern of missile tests and provocations. At the same time that North Korea’s nuclear and missile capabilities continue to expand, we see signs of weakening alliance ties between the United States and the Republic of Korea (ROK) as negotiations for a new Special Measures Agreement have faltered.

Sanghoon Kim spoke with Mira Rapp-Hooper (Council on Foreign Relations) on the current state of the U.S.-ROK alliance and the issue of the credibility of U.S. extended deterrence in the face of a growing North Korean nuclear threat.

What are your observations of the current status of the U.S.-ROK alliance?

The U.S.-ROK ties are significantly strained and far below what we should expect them to be. Given a clear set of shared threats, which is what alliances generally coordinate around and are designed to manage, the United States and South Korea nonetheless find themselves taking different approaches to North Korea and the region more broadly, and it is partly due to problematic alliance management.

First, the United States and South Korea are significantly estranged when it comes to North Korea. We find ourselves in a position where the two allies have basically been conducting separate diplomatic tracks with North Korea with different objectives.

In addition, the U.S. position has been highly focused on trying to further a goal of full denuclearization that is no longer possible. This approach not only seeks an unattainable goal, but also focuses on Kim Jong-un’s ability to deliver nuclear weapons to the U.S. homeland. The Trump administration has continued to push for denuclearization in part because Kim has frozen intercontinental ballistic missile (ICBM) and nuclear testing in the meantime. But this misses the opportunity to formulate a more comprehensive approach that recognizes Kim as a threat to Asia as a region, especially to South Korea.

Of course, the alliance is not primarily focused on the response to the pandemic, but the coronavirus gives us an important lens to view the current state of our relations and why they are so strained compared to what we should expect. The United States had its first known cases of the coronavirus at the same time as South Korea, and yet evidence suggests that there was little cooperation between the allies as the virus spread. South Korea, compared to the United States, did a comprehensive job of both implementing the procedures to try to mitigate the spread of the virus and then implementing widespread testing to control its outbreak further, but the United States did not learn a great deal from its ally as it prepared for the virus to land on its shores. Rather than rallying together at a moment of deep and catastrophic shared threat, we see them clearly estranged.

The deadline for negotiating a new Special Measures Agreement passed long ago, and there is still a big gap between the two sides’ demands. Why has it been so hard to reach an agreement, and what efforts are needed to overcome this deadlock?

It has been difficult to come to an agreement because the U.S. demand is unreasonable. The price tag of $5 billion that was offered to our South Korean ally seems to be an effort to push South Korea to give as much as it possibly can under the threat of having the alliance degrade. It seems to be a public and coercive effort to get more out of our ally, and the negotiations have really been set up to fail in that regard.

The U.S demand may have further intended effects because the United States and Japan will be going through similar negotiations in just a few months’ time. Therefore, Washington may want to demonstrate to both sets of allies that they need to pay up if they are to continue to count on the same level of U.S. support. South Korea is one of the cheapest places on earth to base U.S. troops, and negotiations could have been pursued in a way that is faithful to the alliance and to the current contributions of South Korea. By making more modest suggestions for how South Korea could increase its contributions or, more importantly, by putting new items on the balance sheet that aren’t traditionally considered to be part of the arrangement, the United States probably would have received a higher commitment.

Beyond the issues that are on the negotiation table now, the United States and South Korea cooperate in a number of ways that transcend the discrete defense costs of the alliance. Increasing the scope of what Washington and Seoul consider to be alliance cooperation would leave more room for success in what is already a highly productive burden-sharing arrangement.

President Moon has pledged to complete the transfer of wartime operational control (OPCON) within his presidential term. What implications would this have for the U.S.-ROK alliance?

The question of OPCON transfer has been with the alliance for some time. It is not surprising that President Moon would pledge the full transfer of wartime OPCON, as doing so would signal South Korea’s relative independence, which is consistent with his broader policy. However, the United States and South Korea could erode the deterrence that is necessary for them both against North Korea by expediting this process. If OPCON transfer is accomplished too quickly for the sake of fulfilling a political promise, South Korea could be left in wartime OPCON without the two allies having fully coordinated a new defense and deterrence posture for the environment that will keep the Korean Peninsula safe and stable.

Of course, there are also concerns from the U.S. perspective on the disposition of U.S. troops on the peninsula once OPCON is fully transferred and whether it means that the U.S.-ROK combined command is set to change further in the years to follow. Nevertheless, a conditions-based OPCON transfer is something the allies can manage, but they must share an understanding of what is necessary to defend and deter against the North Korean threat at a time when that threat is quickly changing.

How will China’s growing influence in the region affect the alliance? What is the U.S. response to South Korea tilting more toward China, and what does this mean for the U.S.-ROK alliance?

There’s no question that China’s rise in the region will likely strain the U.S.-ROK alliance as well as other alliances in different ways. But it need not be a deep or insurmountable problem so long as the United States and its allies are able to coordinate their policies and give each other space to pursue their abiding national interests—including, but not limited to, their security relationships.

The United States must understand that every country in Asia has deep economic ties to China and that it does not advantage the United States if its allies feel that they are forced to choose. Even if the ally’s prosperity depends significantly on economic ties with Beijing and security ties with Washington, the United States can still have a very successful alliance system.

Regarding South Korea, we can imagine there will continue to be some gap in Washington’s and Seoul’s views about how centrally China should figure into alliance strategy and strategy more broadly for the region. This is not something that should be anything close to fatal and should not even really be damaging to the U.S.-ROK alliance because Washington and Seoul share visions for what they hope to see from the broader Asia-Pacific. Their visions for what security and stability look like are still broadly aligned, and there is a strong preference for the United States to remain a central military power, even if it’s one of two in the region.

There are growing concerns in South Korea over the credibility of U.S. extended deterrence in the face of a direct North Korean threat to the U.S. mainland. As North Korea’s nuclear weapons technology becomes more sophisticated, how will it impact the credibility of U.S. extended deterrence in South Korea?

The reason that North Korea’s development of a reliable nuclear capability and a deliverable ICBM is so significant is because it forces a technological wedge into extended deterrence.

When an adversary does not have nuclear weapons, the United States can confidently say that it will treat an attack on South Korea as an attack on itself. By committing to come to the defense of South Korea in a prospective war with North Korea, the United States puts its own troops at risk but not its homeland. This is a credible commitment, and the United States has an incentive to act as it says it will because the stability of South Korea—and of Asia more broadly—is very clearly in its defensive interest.

When an adversary like North Korea develops not only a reliable nuclear capability but the ability to deliver it to the U.S. homeland, those incentives change significantly. Once North Korea has reliable ICBMs, it creates a dilemma of whether the United States would be willing to come to South Korea’s aid given the possibility that North Korea could strike the U.S. homeland in return. No one can argue that it is as plausible for the United States to be willing to expose its homeland on behalf of South Korea’s defense as it was before. This development has changed fundamentally the credibility of the U.S. security guarantee.

Nevertheless, the United States continued to have highly effective alliances with NATO throughout the Cold War, despite the fact that the Soviet Union could strike the U.S. homeland. What Washington did was essentially create new political mechanisms, such as a nuclear planning group, through NATO. The United States even changed its own nuclear doctrine to make its entry into a conflict on Europe’s behalf more plausible. Technological decoupling does fundamentally change security guarantee incentives, but the United States has historically used political ties to help right those incentives as best as possible.

The reason that this decoupling problem is especially distressing in the case of the U.S.-ROK alliance is that North Korea’s technological developments have coincided with a political divergence between the allies. Moreover, by conducting summits with Kim that involve very little coordination with South Korea, the United States has basically sent a set of political signals that match up perfectly with the technological dilemma that Kim presented us with—that the U.S. and ROK fates are not intertwined.

The 2018 Nuclear Posture Review states that “expanding flexible U.S. nuclear options now, to include low-yield options, is important for the preservation of credible deterrence against regional aggression.” Would adding new low-yield options enhance the credibility of U.S. deterrence against North Korea?

Low-yield nuclear weapons do not add to the deterrence of North Korea because the United States is basically uncontested in its nuclear capability. Although U.S. assets such as ICBMs and nuclear bombers are based at home, the delivery time to North Korea is extremely short on the order of 30 minutes. There is very little that the United States could accomplish with a lower-yield option placed in the region that it could not accomplish with homeland nuclear assets. Most of our allies recognize that the U.S. nuclear arsenal is highly reliable even when based in the homeland.

However, we should separate the question of whether U.S. nuclear assets are homeland-based or forward-deployed from the yield of the nuclear weapon itself. Historically, allies have thought of lower-yield nuclear weapons as more likely to be forward-deployed. But if one believes that low-yield options are useful, it is also because one believes that there is a possibility of introducing nuclear weapons into a conflict with North Korea and that the United States and South Korea gain something strategically from having lower-yield options.

If we want to ask ourselves what the value of a lower-yield nuclear weapon might be, we should ask why we think North Korea might use nuclear weapons in the first place—as this presents the most likely context in which the United States would consider nuclear use. All evidence indicates Kim Jong-un understands very well that a decision to use nuclear weapons would end the regime. So, if Kim uses his nuclear weapons first, he likely thinks that the regime is in absolute jeopardy. Therefore, the use of lower-yield nuclear weapons would probably not change his calculation.

In fact, nuclear weapons remain an absolute last resort in conflict, and they should remain intended primarily for deterrence purposes, which still makes them compatible with extended deterrence and allied assurance. I have not seen a case that convinces me—either because of their actual utility as a component of the U.S. nuclear arsenal or because of their specific utility in a conflict on the Korean Peninsula—that lower-yield nuclear weapons would add more credibility to the U.S.-ROK alliance.

Forward basing and the presence of the United States Forces Korea on the peninsula are also intended to serve as a deterrent against North Korean conventional provocations. Has U.S. conventional extended deterrence been credible in curbing low-level provocations?

The U.S. conventional extended deterrence generally has been credible. It’s important to remember that deterrence can accomplish different things at different levels. While the U.S. conventional deterrence on the Korean Peninsula and the combined U.S.-ROK posture has been extremely successful in deterring a second Korean War—its primary purpose—the same force cannot be expected to deter every kind of provocation.

Part of the reason North Korea chooses provocations, such as the sinking of the Cheonan or the shelling of Yeonpyeong Island, is that the U.S.-ROK posture is not centrally focused on the deterrence of those activities. Instead, it’s focused on preventing North Korea from crossing the 38th parallel or using nuclear weapons to radically transform the political settlement on the peninsula. Pyongyang is more likely to be able to get away with some coercion knowing that it will be harder for the alliance to respond at this level.

The U.S.-ROK alliance needs to upgrade its conventional posture with the expectation of continued low-level provocations. Focusing its efforts on such provocations enables North Korea to achieve its coercive aims more effectively. But North Korea’s deliverable nuclear weapons also radically transform the way the alliance thinks about fighting wars. Working through conventional strategy changes that come under the shadow of North Korea’s nuclear weapons is therefore a necessary part of updating the alliance.


Mira Rapp-Hooper is the Stephen A. Schwarzman Senior Fellow for Asia Studies at the Council on Foreign Relations and author of the forthcoming book Shields of the Republic: The Triumph and Peril of America’s Alliances (June 2020).

This interview was conducted by Sanghoon Kim, a Korea Foundation Research Fellow with the Political and Security Affairs group at NBR. This edited transcript is taken from the video interview The Credibility of U.S. Extended Deterrence on the Korean Peninsula.