For the first time in 20 years, the United States and South Korea both have left-of-center presidents. The pairing of President Joe Biden and President Moon Jae-in might seem at first blush to forecast a stronger alliance, especially after President Donald Trump’s abrasive leadership style cast doubt on the bedrock of Washington’s relationship with Seoul: mutual respect and the United States’ commitment to South Korea’s security. But there are fissures in the U.S.–South Korean alliance that will outlast Trump.

In contrast to their conservative counterparts, the progressives in Moon’s government wish to maintain a significant degree of autonomy from big powers (notably the United States and Japan). They are also sympathetic toward North Korea and China. Both impulses portend friction with the incoming Biden administration, which seeks to rally a coalition of democracies to counter China and is inclined to pursue a tougher policy toward Pyongyang than Moon. South Korea under Moon will be Biden’s linchpin ally in the Indo-Pacific, but at the same time it could be the weakest link in the planned democratic coalition. Seoul will also seek to reject additional international sanctions against the North, initiate a speedy peace process, and overlook Pyongyang’s human rights violations—all of which could rankle Washington.

Any discord between the United States and South Korea could put at risk the security of both the Korean Peninsula and the broader region, especially as China and North Korea seek to gradually erode the United States’ system of alliances. The Biden and Moon teams must therefore hold a series of frank and regular conversations, or else they will be headed for a bumpy ride. Washington and Seoul still have an opportunity to strengthen their alliance during the Biden and Moon administrations—but doing so will require a delicate dance.


Moon’s government has been reluctant to participate in global initiatives led by other democracies, especially those aimed at strengthening the rules-based international order, often to the confusion of U.S. and European officials. Moon’s foreign policy is shaped by domestic political goals—inter-Korean reconciliation, Korean nationalism, and autonomy from big powers—that explain why his government prioritizes inter-Korean relations and self-reliance over the U.S.–South Korean alliance. Moon and his supporters believe that if Seoul’s relationship with Pyongyang improves, South Korea can depend less on the United States and that the two Koreas can together pressure Japan to repent for its wartime and colonial sins.

The Moon government’s parochial aims have other important consequences. South Korea does not want to be forced to choose a side in the intensifying competition between the United States and China, since alienating either power could adversely affect its security and its economy. For example, in October of last year, the United States called on its allies, including South Korea, to ban China’s Huawei. Meanwhile, Beijing has been pressuring Seoul to bolster their cooperation on 5G, artificial intelligence, and big data. Caught between two powers, South Korea has avoided explicitly taking a side in the dispute thus far. Instead, it has reportedly pushed back against U.S. pressure to ban Huawei while also acknowledging the importance of the United States’ “Clean Network” initiative, a U.S.-led telecommunications network that aims to be an alternative to Chinese networks such as Huawei.

In general, Seoul prefers to maintain a degree of ambiguity in its relationship with China—something many Americans perceive as indecisiveness or aloofness toward the United States. This tendency is even more pronounced among the Korean progressives who make up Moon’s base of support. Biden’s calls for an alliance-based approach to China and trilateral cooperation among the United States, Japan, and South Korea to deal with North Korea could therefore pose a dilemma for Moon. South Koreans have concerns about participating in multilateral initiatives that seem aimed at containing Beijing, not least because they could result in more Chinese bullying of South Korea. Fearing backlash from Beijing as well as his domestic supporters, Moon will need convincing geopolitical and political justifications to join multilateral security initiatives that deal with a rising China and take on North Korea.


In exchange for participating in Biden’s multilateral initiatives, Seoul may bargain for the U.S. president to make an early diplomatic overture to North Korea. Biden pledged to engage in “principled diplomacy,” which suggests that any U.S. concessions, such as relieving sanctions,  will be contingent on Pyongyang’s agreement to meet certain conditions, such as taking credible steps toward denuclearization. But Moon and his progressive supporters believe a different approach is more effective. They argue that granting major concessions that meet North Korea’s demands without requiring conditions can persuade North Korea to denuclearize.

Moon is pressed for time. He is driven by the desire to establish peace on the Korean Peninsula before he vacates office in May 2022, even if that means tolerating some level of aggressive North Korean behavior and incomplete denuclearization. To avoid aggravating Pyongyang (and to help resume inter-Korean projects), the Moon government will oppose enforcing existing sanctions and designating new ones, particularly in the absence of a major North Korean provocation. It will also try to persuade Washington to lift some sanctions.

To secure his legacy as a peacemaker, Moon will want to facilitate an early U.S.–North Korean summit and initiate a peace process, beginning with a declaration that formally ends the war between North Korea and the United States and concluding with North Korea’s denuclearization and a peace treaty. U.S. policy has consistently been to insist on denuclearization before peace. There are ways to pursue both processes in tandem, but Washington and Seoul should first push for significant denuclearization measures. Without them, Washington risks signing a premature peace agreement with a permanently nuclear-armed state.

There are fissures in the U.S.–South Korean alliance that will outlast Trump.

Seoul’s biggest challenge will be persuading Biden to meet with North Korean leader Kim Jong Un early on while convincing Pyongyang to credibly commit to denuclearization and to offer a proportionate concession for face time with a sitting U.S. president. Seoul is pushing for a four-way summit between the United States, South Korea, North Korea, and Japan at the 2021 Tokyo Olympics, in addition to advocating for a bilateral summit between Biden and Kim. But Kim has made clear that his precondition for any talks is the elimination of “hostile U.S. policy.” By that he means termination of U.S.–South Korean defensive drills, removal of sanctions, and an end to human rights criticisms and name-calling. Kim has also demanded that Seoul refrain from buying high-tech weapons for its defense and that it essentially break its alliance with Washington by ending joint U.S.–South Korean military exercises and eventually withdrawing U.S. troops from the peninsula.

The Biden administration will work to strengthen its military presence in Asia in order to deter North Korean provocations and Chinese aggression. On the one hand, Seoul will likely be hesitant or unwilling to join such an effort, since the Moon government and its progressive base believe deterrence could interfere with peace efforts. South Korea prefers to continue scaling down U.S. missile defenses and combined U.S.–South Korean military drills to avoid aggravating China and North Korea. On the other hand, Seoul still needs the joint drills to transition wartime control of the armed forces from the United States to the South Korean military within Moon’s presidential term, to achieve the country’s goal of “military sovereignty.” Seoul is thus caught in a bind between appeasing North Korea and satisfying the Biden administration.

Another point of potential friction is North Korea’s human rights record, over which the United States and South Korea are already at odds. South Korean progressives prefer turning a blind eye to North Korean human rights violations out of fear of upsetting Pyongyang and have abstained from voting on UN resolutions about North Korean violations in the past. Most recently, South Korea’s National Assembly, in which Moon’s progressive ruling party enjoys a supermajority, passed a law in December of 2020 banning the decades-long practice of sending leaflets and balloons containing food, South Korean news, and information about the outside world across the demilitarized zone. Violators of the new law will be sentenced to up to three years in prison or fined 30 million won ($27,400). Freedom of expression is a core democratic value for the United States, and banning leaflets would counter long-standing bipartisan efforts in Washington to provide North Koreans with access to outside information.

Washington and Seoul must quickly resolve their differences and work together to confront shared challenges, including China’s aggression and North Korea’s advancing nuclear weapons capability. Too much is at stake to let differences fester. The Biden and Moon teams may not be in lockstep at first. But by focusing on shared values and commitments—to democracy and a rules-based international order—they can shore up a resilient alliance.

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  • DUYEON KIM is Adjunct Senior Fellow at the Center for a New American Security and Columnist at the Bulletin of the Atomic Scientists.
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