Jennifer Kavanagh is a senior fellow & director of military analysis at Defense Priorities.
A political scientist by training, Kavanagh has spent her career studying U.S. national security and defense policy. Kavanagh’s research focuses on U.S. military strategy, force structure and defense budgeting, the defense industrial base, and U.S. military deployments and interventions.
Previously, Kavanagh was a senior fellow in the American Statecraft Program at the Carnegie Endowment for International Peace. She also worked as a senior political scientist at the RAND Corporation, where she led projects for defense and national security clients. She served for three years as director of RAND’s Army Strategy program. Her work has been published in Foreign Affairs, The New York Times, Foreign Policy, Journal of Conflict Resolution, The Washington Quarterly, Lawfare, Los Angeles Times, and War on the Rocks, among other outlets.
Kavanagh received an AB in Government from Harvard University and a PhD in Political Science and Public Policy from the University of Michigan. She is also a term member of the Council on Foreign Relations and an adjunct professor in the Security Studies Program at Georgetown University.
Section 1. South Korean Perspective: Critical Examination of Security Vacuums & Domino Effects
1. Termination of the Mutual Defense Treaty & Nuclear Proliferation Incentives:
You propose terminating the U.S.-ROK Mutual Defense Treaty, withdrawing U.S. Army and Marine forces from South Korea, and transitioning to a narrower security partnership. However, if Washington withdraws its extended nuclear deterrence (nuclear umbrella), South Korea would face intense pressure to pursue an independent nuclear weapons program for its survival. Wouldn’t a nuclear-armed South Korea trigger a regional nuclear domino effect (e.g., Japan, Taiwan), posing a far more existential threat to U.S. national interests and the global nonproliferation regime?
I agree that if the United States pulls back from its current security commitments, it is likely that South Korea and possibly Japan will pursue nuclear weapons. However, I do not see this as a threat to U.S. interests and on net, would prefer some friendly nuclear proliferation to a future in which the United States maintains its current security commitments.
There are risks that will come with nuclear proliferation, but I believe that it some increase in the number of nuclear weapons states is inevitable. First, the U.S. use of military force against non-nuclear powers including Iran, Libya, and Iraq has taught U.S. competitors that the only way they can be safe is to build a nuclear program of their own. President Trump has said as much in recent speeches, stating that he would behave differently toward Iran if Iran had a nuclear weapon. Second, U.S. overextension and the military vulnerabilities that the United States has shown in the Middle East have already caused concerns among U.S. allies about the ability of Washington to meet its security commitments. The reality is that the United States is very limited in the military support it can provide to allies today, due to resource constraints and erosion of military readiness and stockpiles. As a result, many U.S. allies are already talking about getting their own nuclear weapons, and this trend will continue even if the United States does not formally narrow security treaties or change posture as much as I recommend.
I also think that some proliferation would be acceptable, could be stabilizing, and would not damage U.S. interests. If the United States can give up expansive security commitments and entanglements that might pull it into a major power war that it cannot afford to fight, it will be better off, even if some proliferation occurs. Proliferation is likely to be limited, preventing the worst-case scenario cascades people warn about. Some states will not want nuclear weapons—some will find these programs too expensive or too technically difficult. Of course, proliferation would come with some risks, but these could be managed by the United States and other nuclear powers through the development of a new nuclear safety regime, that includes safeguards and transparency mechanisms.
2. DPRK Miscalculation & Risk of Contingent Conflict:
Retreating to the Second Island Chain signals a strategic drawdown. Do you believe your assessment fully accounts for the risk that the Kim Jong Un regime might interpret this move as a complete abandonment of U.S. commitments, thereby emboldening Pyongyang to launch lethal military provocations or an invasion? If a major conflict erupts on the Korean Peninsula, would passive observation from the Second Island Chain truly serve U.S. economic and security interests?
I think South Korea is strong and wealthy and could defend itself against North Korea. It already has conventional military advantages against North Korea and the remaining capability gaps are ones that Seoul is very capable of filling relatively quickly.
I also think the scenario posed here is very unlikely. North Korea has improved its strategic situation significantly, building closer ties with Russia and expanding its influence. I see little indication that it is still focused on trying to force unification on South Korea. Surely Kim Jong Un understands what a conventional war would mean for North Korea and there would be pressure from China and Russia against nuclear use.
As importantly, that the United States cannot now afford a war on the Korean Peninsula. The United States has a one war military and after the war with Iran, it will be some time before the country can fight another major war. Right now, all U.S. security promises are a bit hollow due to resource limitations. Even when it does reconstitute, the United States will have to focus its still constrained resources against highest priority threats, specifically China, not North Korea. The United States now faces a situation where it must give up lower priority commitments, especially those like that in South Korea where allies are capable of self-defense.
Phasing out the military presence and defense commitment to South Korea would be better for the United States and for South Korea. The United States could conserve resources and reduce its risk of entanglement. Meanwhile, South Korea could properly plan for a future in which it would be operating mostly on its own.
3. Feasibility of the 3-to-8-Year Transition Window (2030–2035):
Your proposed implementation roadmap outlines completing major U.S. force withdrawals by 2030 and ending treaty commitments by 2035. Given the immense industrial, structural, and financial adjustments required for Seoul to build an entirely autonomous conventional deterrence capabilities against North Korea, isn’t a 3-to-8-year timeline overly aggressive and impractical for South Korea’s defense posture?
No, I don’t think it’s overly aggressive. South Korea already has conventional superiority over North Korea and has a robust and growing defense industry to help fill remaining capability gaps. It is already investing in improving its combat support capabilities, indigenous ISR assets, and command and control. A timeframe of about 5 or so years is very realistic to transition South Korea to a position near defense self-sufficiency. Moreover, the United States and South Korea are already working toward completing OPCON transfer within the next 3-5 years, and already South Korean forces have assumed more responsibility for frontline defense.
If required and in U.S. interests, the United States could offer some enabling support to South Korea beyond in this timeframe and in case of a crisis, but such support should be provided on a limited term and transactional basis, not an expansive security guarantee. My recommendations allow for such flexible partnerships to continue. Seoul could also build partnerships with other regional partners if it chose to fill remaining gaps as needed. My view is that South Korea is already very prepared to defend itself, so I see the timeline I offer as realistic.
Section 2. U.S. Perspective: Strategic Realism & Cold Calculations of National Interest
4. Expansion of Chinese Regional Dominance & Economic Access:
If the U.S. significantly reduces its forward-deployed military presence along the First Island Chain, how do you evaluate the likelihood of China expanding its dominance over critical maritime sea lines of communication (SLOCs) in the East and West Seas and the Taiwan Strait? If Beijing consolidates regional hegemony, how can the U.S. guarantee “economic access to Asian markets,” which you highlight as a core U.S. national interest?
The reality is that China could already dominate and restrict access to the South China Sea and Taiwan Strait, even today with the current U.S. military presence. This is because of its geographic and maritime advantages. China’s naval power is expanding rapidly. The United States and allies have long hoped that having a strong U.S. military presence on the first island chain would contain Chinese power but increasingly, China is able to project power deeper into the Pacific even with U.S. military presence along the first island chain.
But China has not shown any intent to cut off the access of other countries to trade routes in the South China Sea or Taiwan Strait or other waters close to its coast. This is because imposing such limits would harm Chinese interests most of all. China is a trade dependent nation, and it would be an act of self-harm to try to block these waters.
But even if China decided to restrict access to waters closest to its shores, there are a diversity of sea routes across East and Southeast Asia that the United States and other regional powers could use as alternatives. We have seen in the Middle East that commercial traffic can re-route quickly, to bypass the Bab el-Mandeb. The same is true in Asia, where there are a number of possible passage ways through southeast Asia. Large bodies of water to the east of Japan, would also be very difficult for China to control fully and sea lanes in this part of the region could be defended from the second island chain if required.
Consolidating regional hegemony would be very difficult for China, even if the United States pulled most forces back from the first island chain. The region’s geography and vast distances would make territorial conquest extremely difficult. Just taking Taiwan will not be enough. China would also have to seize the Japan at least. Countries like Japan and South Korea also seem to me to have no interest in being vassals of China. They are much more likely to try to balance Chinese power if the United States pulls back, investing in their own self-defense. China might instead try to use political and economic coercion to dominate the region, but once again, it probably could do this now, if it chose. If the United States wants to counter this outcome, it does not need military power, but a region-wide economic strategy. Some argue that without military power and security guarantees, the United States would lose its economic relationship with Japan and South Korea. But there is just no evidence that this is the case.
5. Vulnerability of the Second Island Chain (Guam & Micronesia):
Consolidating U.S. forces in the Second Island Chain (Guam, Saipan, Palau) leaves them within the operational range of China’s intermediate-range missiles (e.g., DF-26) and strategic bombers. Doesn’t concentrating high-value assets onto narrow island targets create high-density target zones, thereby increasing missile defense burdens rather than mitigating tactical risk?
If bases on the second island chain are vulnerable to Chinese attacks, what does that say about bases on the first island chain which are so much closer to mainland China? China has many more short range ballistic and cruise missiles that can target these bases than longer range ones that can hit Guam or Palau. Bases along the first island chain cannot help with dispersion of assets if they become effectively unusable in a conflict. Look at the Middle East. The United States had dozens of bases and essentially none were survivable. They became targets and the United States was forced to abandon them and consolidate assets farther away from Iranian territory. Continuing to believe that first island chain bases are operational or strategic assets after observing what happened during the war with Iran makes no sense and completely ignores the many lessons of that war.
If it pulled back to the second island chain, the United States would have to invest heavily in infrastructure and hardening along bases in these locations and probably rely more on carrier-based power projection. But with the smaller set of commitments, I lay out in the paper, it would also need fewer assets forward in the region.
Furthermore, pulling back to the second island chain and narrowing U.S. commitments would substantially reduce the risk of a war between the United States and China that would involve Guam or Palau. A China that does not have U.S. military forces right off its coast is a China that may be more patient toward Taiwan and feel less need to assert itself militarily in its near abroad and against the United States. If the United States seems likely to stay out of regional disputes, I think it is unlikely that China would attack bases on what is U.S. territory on the second island chain. The overall risk of conflict and threats to second island chain bases would be lower.
6. Costs to Global U.S. Alliance Credibility:
If Washington unilaterally scales back or terminates defense treaties with treaty allies like South Korea, how would other Indo-Pacific allies (Japan, Australia, Philippines) or NATO partners perceive U.S. security commitments? How do you factor the reputational cost of perceived alliance abandonment into your strategic calculations?
I think U.S. security commitments in Asia and elsewhere are increasingly hollow. The United States maintains a network of security guarantees, to several dozen countries, yet we see in the Middle East that it is even unable to defend its own bases. These promises to countries like South Korea and NATO allies are simply no longer credible, nor can they be resourced. A decision to narrow U.S. military commitments would be an acknowledgement of this reality, that the U.S. strategy is insolvent and that it must retrench to focus on defending its highest priority interests. Maintaining empty security commitments benefits no one. It leaves the United States exposed and allies unprepared. Security guarantees also distort global politics. They create moral hazard, discouraging allies from investing in their own defense and encouraging them to adopt foreign policies that do not match their geopolitical circumstances. It is normal and should be expected that countries build defense self-sufficiency.
I have argued that the United States should phase out all of its security guarantees, to other countries in Asia and to NATO allies. For this reason, I don’t worry that much about the credibility or reputational concerns you mention. I also don’t see this as abandonment. States should not expect the United States to defend them forever. As current U.S. allies come to realize that the United States does not have the military power or the political will to come to their defense, they will have to decide how best to adapt, either by spending more their military or by seeking out other partners.
That said, the United States should endeavor to stay friends with current allies, even if the security relationship changes. Transitions should be managed and transparent, limited security cooperation and joint ventures in the defense space might continue. Economic investment and engagement could increase. The United States pulling back should never be framed as a punishment for allies, but rather a necessity for the United States and its interests.
Section 3. Strategic Leverage & The “New Paradigm” in ROK-U.S. Relations
7. Leveraging World-Class South Korean Defense Industrial Capacity (K-Defense):
For your strategy to succeed, First Island Chain nations must bolster their self-defense capabilities. South Korea possesses a world-class defense industrial base capable of mass-producing advanced conventional hardware (K2 tanks, K9 self-propelled howitzers, FA-50 light fighters). Should U.S. forward posture decline, how do you assess integrating South Korea’s defense manufacturing capacity into broader U.S. and allied defense supply chains?
This integration is already happening and could continue. Defense industrial cooperation between South Korea, the United States, and countries like Japan or in Europe is not premised on the forward basing of U.S. military forces or security guarantees. Joint ventures could continue, and South Korea is a great defense partner for European states and other East Asian partners looking to purchase high quality weapons systems at reasonable prices and on rapid timelines. Building defense production capability and accessing a diversity of defense suppliers outside the United States is important for countries looking to build self-sufficiency, especially since the U.S. defense industrial base is overstretched.
8. South Korea as a Critical Pillar in Tech & Industrial Supply Chains:
Even with a reduced military footprint, winning tech-economic competition with China requires South Korea’s capacity in semiconductors, advanced batteries, and shipbuilding. Within your framework of “narrower and flexible partnerships,” what economic or technological incentives should Washington offer Seoul, and how can South Korea’s unique capabilities (e.g., naval ship MRO/repair capabilities for the U.S. Navy) be leveraged?
I do not think “winning the tech-economic competition” is the right framing. I am not sure this is something either side can win in the way the question supposes. There will be competition between the two powers, but the United States and China will need to accept mutual vulnerability in this domain and also seek opportunities for cooperation.
But more importantly, cooperation in the economic and defense industrial domains between the United States and other regional powers does not depend on military presence and security guarantees. The United States can offer South Korea better trade terms, more U.S. investment in the South Korean economy, or incentives to invest in the United States. The United States can continue to work with South Korea on defense projects, including joint ventures and projects in emerging technology, where interests align, though with my proposed strategy, U.S. military requirements would decline—including the need for assistance in shipbuilding and repair. Greater technology transfer and sharing in the defense space would be another way to bolster economic ties between the two countries without military presence or security guarantees. The United States does need a better and more coherent economic strategy in the region that reduces trade barriers and doesn’t use tariffs as punitive tools, as Trump has done.
But my report also recommends reducing U.S. manufacturing and tech dependence on the foreign markets in Asia. The United States should work to reshore semiconductor production and invest much more in regional trade and economic networks in Latin America than it does today.
9. Alternative Paradigm: Near-100% Fair Burden-Sharing:
Rather than a complete termination of the Mutual Defense Treaty, wouldn’t a “restructured alliance”—where South Korea covers nearly 100% of USFK stationing costs and assumes full operational control (OPCON) in peacetime, while the U.S. retains strategic extended deterrence—serve as a more pragmatic compromise that reduces U.S. risks while safeguarding national interests?
For me, the problem with having forces in South Korea is not the cost, but the risk and burden. If the United States has military personnel in South Korea and there is some crisis, the United States will be implicated. The options available to the president would shrink and the United States might be dragged into a conflict that is not in U.S. core interests due to inertia or politics. This would mean accepting risk in other areas or sacrificing much more important interests—if the United States fights a war in South Korea, it will be unable to respond to truly existential threats given resource constraints. The reason I suggest pulling back from South Korea, in terms of posture and commitments, in other words, is because the risk incurred by maintaining the status quo is greater than the interests at stake. In a world in which the United States cannot resource all of its commitments, this is unacceptable. Furthermore, I don’t think U.S. presence is necessary. I believe that South Korea is ready to defend itself in the conventional domain.
Once you remove the ground forces, the nuclear commitment is no longer credible. My view is that extended deterrence is already a bluff (it’s hard to believe a U.S. leader today would sacrifice a U.S. city to defend a foreign one), but once U.S. ground forces leave, then the U.S. nuclear umbrella clearly no longer credible. I understand that this means that South Korea may think seriously about pursuing nuclear weapons, and as noted at the start of this interview, I still think that outcome is better for the United States than maintaining the current set of commitments.
