U.S.-ROK-Japan Trilateral Security Alliance


The trilateral security alliance between the United States, the Republic of Korea (ROK), and Japan is the most consequential security alliance for the U.S. today outside of the North Atlantic Treaty Alliance (NATO). The trilateral alliance traces its roots back to the Cold War when the U.S. made heavy military and economic investments in both nations following World War II and the Korean War that were primarily focused on containment of the Communist threat by balancing against regional actors including the Soviet Union, the People’s Republic of China (PRC) and North Korea. Even after the collapse of the Soviet Union and the triumph of Western-led capitalist nations over communism, the founding mission of the alliance structure to balance against regional adversaries still holds true today.

U.S.-Japan Relations

The modern U.S.-Japan partnership was built from the ashes of WWII, where after a bitterly-fought war in the Pacific theater marked by atrocities committed by Imperial Japanese forces and the dropping of two atomic bombs on civilian populations, Japan was forced to surrender and renounce its right to wage war in any capacity (Article 9 of the postwar Constitution). However, the outbreak of the Cold War and regional proximity of the Soviet Union forced the U.S. to transition its relationship with Japan from a wartime occupation of a defeated enemy to a robust security alliance in the span of a few years. This was marked by the signing of the Security Treaty of 1951 and the Treaty of Mutual Cooperation and Security in 1960.[1]

Now under the protection of American military bases and personnel, Japan was free to begin rebuilding its government and society. Soon after the war ended, many imprisoned high-ranking military and political officials from the Imperial government were pardoned by the U.S. to rejoin the recently reformed Japanese government and prevent a nationwide collapse after the end of occupation. A number of the released prisoners who served the Imperial Diet during the war joined the newly formed Liberal Democratic Party (LDP) in the National Diet, which has effectively controlled the government since its founding in 1955. While they did not make up the majority of the party, their prior experience and political expertise influenced the party greatly for decades to come.

U.S.-Japan relations grew stronger in the decades following, and from 1954 to 1992, Japan experienced exponential economic growth during a period known as the “economic miracle.” For over four decades, Japan reigned as the second-largest economy behind the United States until being overtaken by China in 2010. However, Japan’s meteoric economic rise ended in 1991 when Japan’s asset price bubble crashed and resulted in a period of economic stagnation known as the “Lost Decade.”

Today, the U.S. maintains exclusive use of 85 military facilities along the Japan archipelago — 33 of which are located on the small southwest Japanese island of Okinawa — manned by approximately 54,000 U.S. military personnel.[2] The American troop presence in Japan is the largest in the world outside of the continental U.S. Rising tensions and the Trump Administration’s continued emphasis on the Indo-Pacific has cemented Japan’s role as the bedrock of American power projection in the region.

Article 9 of Japan’s Constitution

China’s increasing military strength coupled with more frequent provocations from North Korea over the past few years has resulted in closer U.S.-Japan ties as well as a growing desire within certain ranks of the LDP to expand Japan’s constitutional defense authorities. Enacted as part of Japan’s postwar constitution, Article 9 specifically prohibits Japan from maintaining the capacity to wage war.


(1) Aspiring sincerely to an international peace based on justice and order, the Japanese people forever renounce war as a sovereign right of the nation and the threat or use of force as means of settling international disputes.

(2) In order to accomplish the aim of the preceding paragraph, land, sea, and air forces, as well as other war potential, will never be maintained. The right of belligerency of the state will not be recognized.[3]

Over the past 70 years, multiple reinterpretations by the government have allowed Japan to exploit certain loopholes in order to expand its arsenal and defense authorities. These include:

· Considering the Self Defense Forces an extension of the national police force, not a formal military body and therefore not considered ‘war potential’;

· Defining war potential as exceeding the minimum level required for self-defense; and

· Allowing the SDF to use military force to defend allies if war was declared upon them, independent of whether Japan itself was being directly attacked as well.

The U.S. has historically pushed for greater defense commitments from Japan, especially in the wake of the terrorist attacks on September 11, 2001. However, Japan’s immediate neighbors China, South and North Korea continue to harbor deep skepticism and reservations about Japan’s slow turn away from pacifism stemming from their experiences of aggression and brutal occupations under Imperial forces during WWII.

U.S.-ROK Relations

U.S. relations with the Republic of Korea first began after the end of WWII when the Korean Peninsula found itself divided at the 38th parallel between a Soviet-occupied North and a U.S.-occupied South. In 1950, North Korean forces invaded the ROK and sparked what is known as the Korean War. The U.S. and a United Nations coalition of 16 countries defended the ROK during a three-year conflict that resulted in millions of fatalities. The conflict eventually ended in a stalemate between North and South at the 38th parallel, now known as the Korean Demilitarized Zone (DMZ). Despite signing an armistice in 1953 to cease hostilities, both North and South have yet to declare a formal end to the war.

Following the end of the conflict in 1953, the U.S. and South Korea signed the U.S.-ROK Mutual Defense Treaty which commits both nations to come to the other’s aid if either is the victim of an external attack and allowed the U.S. to station military forces on the peninsula in consultation with the South Korean government. This provided the foundation for U.S.-ROK defense cooperation in the following decades in responding to regional threats from North Korea, the Soviet Union, and Communist China.

The U.S. currently maintains a troop presence of 28,500 in South Korea, comprised predominantly of Army personnel. Camp Humphreys houses a majority of these troops and is the largest U.S. overseas military base in the world.[4] Since 1957, South Korean and American forces on the peninsula have operated under the control of the United States Forces Korea (USFK), a sub-unified command of United States Indo-Pacific Command (USINDOPACOM). USFK operational control (OPCON) currently sits in the hands of an American general and semi-integrated command structure between the U.S. and South Korea. One of the goals of South Korea has been to transition wartime operational control of USFK to a binational command led by a South Korean general and a U.S. deputy. South Koreans see OPCON as crucial to cementing ROK sovereignty and gaining recognition for the gains in economic and military strength made by their country since the Korean War.

Burden Sharing Negotiations

Like Japan, both the U.S. and the ROK share the cost of hosting U.S. forces to defend South Korea. This is accomplished under a mechanism known as the Special Measures Agreement (SMA) which is negotiated and renewed every five years and determines the share of the cost each country will shoulder.

The Trump Administration has been vocal about the need for South Korea to shoulder more of the cost of hosting U.S. troops on the peninsula. Leading into negotiations to renew the SMA in 2019, the Trump Administration reportedly asked South Korea to increase its annual contribution by roughly 50%, while South Korea countered with a 13% increase. The two sides have so far failed to reach an agreement and remain at a wide impasse over requested contribution amounts. This has resulted in massive furloughs and suspended defense infrastructure projects, all of which severely hamper military readiness of USFK forces. The absence of an SMA agreement continues to be one of the most pressing and controversial issues between the U.S. and South Korea.

Japan-ROK Relations

The relationship between Japan and the Korean peninsula has been tenuous in the best of times, and outwardly hostile more often than not. The history between the two nations is long and filled with cultural exchange, political confrontation, and military conflict. The Korean peninsula has historically served as the gateway between Japan and the greater Asian continent through China. As a result, Korea as a kingdom and a nation state have often been occupied and trampled through centuries of warfare between Chinese and Japanese empires seeking to invade each other.

This cycle entered the modern age in 1895 when the Empire of Japan defeated the Qing Dynasty of China for primary control over Joseon Korea during the First Sino-Japanese War. The Treaty of Shimonoseki cemented China’s defeat and forced the Qing dynasty to formally forfeit control over Korea. Korea’s independence was short-lived, as competition between Japan and Russia for influence on the peninsula led to the Russo-Japanese War in 1904. Japan’s victory in 1905, and their declaration of Korea as a protectorate of the Empire, signaled a major shift in regional power towards Imperial Japan for the next 40 years under a harsh occupation until the end of WWII in 1945.

Today, many in Japan and South Korea view the other country negatively. In a poll conducted in 2019, 20% of Japanese respondents held a positive view of South Korea, while 49.9% held a more negative view. Similarly, 31.7% of South Koreans viewed Japan positively, while 49.9% of respondents held a negative view of the country.[5] Negative views are primarily influenced by frustration over “South Korea’s continued criticism against Japan on historical issues” or a lack of “remorse over Japan’s past wartime aggression.”[6]

Posture Towards Regional Adversaries

North Korea

Responding to threats from North Korea remains the most unifying issue for the Japan-ROK relationship, even though both powers disagree on the right mix of carrots and sticks in containing threats. The U.S.-ROK-Japan alliance structure currently maintains multiple agreements for intelligence sharing and collaboration, including the Trilateral Intelligence Sharing Agreement (TISA) and the General Security of Military Information Agreement (GSOMIA). Both Japan and South Korea engage extensively with the U.S. on security cooperation regarding North Korea, sometimes with similar goals of de-escalation and nuclear deterrence, and other times with more nationalistic goals such as the reuniting of Korean families separated by the DMZ and the safe return of kidnapped Japanese citizens being held in North Korea.

All three nations have substantial ballistic weapons defense (BMD) capabilities deployed in the region to counter missile threats from North Korea. While increased trilateral BMD cooperation would greatly boost deterrence capabilities towards North Korea, several hurdles remain. Japan is currently an enthusiastic participant in U.S.-led BMD efforts, but South Korea faces significant pressure from Beijing over fears that a united trilateral BMD front could be used to threaten China. In 2016, South Korea made a rare exception to its policy of avoiding conflict with the PRC by deploying the Terminal High Altitude Defense (THAAD) system within the ROK for strictly defensive purposes against North Korea, prompting China to exert economic pressure which cost South Korean businesses billions of dollars. This resulted in South Korea conceding “three no’s” to China in exchange for a return to normal — no additional THAAD deployments, no participation in a U.S.’-led missile defense network, and no formal establishment of a trilateral military alliance with the U.S. and Japan.[7] Therefore, South Korea has maintained an independent BMD capability that is not tied to the U.S. or Japan regional architecture.

Due to its unique relationship with North Korea, South Korea has more incentive to offer strategic incentives to the North in exchange for de-escalation, strengthened ties, and reuniting Korean families divided across the DMZ. Many South Koreans also still strive for an eventual reunification of the Korean peninsula and realize that they will need the cooperation of North Koreans to make that goal a reality. By contrast, the primary concern of the U.S. and Japan is stability and security in the region and are more willing to use more confrontational tactics to achieve concessions from North Korea.


While South Korea’s relationship with Russia formally began in 1990 and can largely be viewed in the context of containing North Korea and siding with the U.S., Japan has a much more nuanced relationship with Russia. Strains between the two powers date back to strategic competition between the Japanese and Russian empires for control in Northeast Asia in the early 20th century, particularly in the Russo-Japanese War in 1904 and in WWII. As a result, Japan maintains several outstanding territorial disputes with Russia, including the ongoing dispute over the Kuril chain of islands.[8]

A majority of Japanese people view Russia unfavorably (64% unfavorably, 26% favorably). Younger generations in Japan aged 18–29 tend to have an increasingly positive view of Russia (53%) compared to their elders (16%).[9] However, Japan still sees Russia as an important security presence in balancing between pressures from China and North Korea. Despite Western sanctions on Russia following the invasion of Crimea in 2014, Japan has continued to engage with Russia constructively on military cooperation, Japanese investment in Russia, and cultural exchange.


Japan and South Korea diverge significantly on their respective relationships with China. The ROK and PRC established formal diplomatic relations in 1990. Until then, the PRC and ROK only officially recognized North Korea and the Republic of China (Taiwan) respectively. Since then, relations have warmed significantly between the two nations leading to closer diplomatic, economic, and cultural ties. By 2004, China had become South Korea’s largest trading partner and in 2015 (following the implementation of the U.S.-South Korea Free Trade Agreement (KORUS FTA) China and South Korea finalized the China-Republic of Korea Free Trade Agreement.[10]

South Korea’s policies towards China are among the most nuanced of all U.S. allies in Asia and often seeks to hedge its bets between Washington and Beijing. This stems from several realities South Korea faces, including China’s outsized military advantage, South Korea’s significant economic reliance on China, and the need for Chinese cooperation in containing North Korea (cooperation with China is also the only path forward to unification of the Korean peninsula given North Korea’s long border with northern China).

In the great power competition between the U.S. and China, South Korea has suffered significant collateral damage to its trade and industry as it is increasingly forced to choose sides. While South Korea remains inherently skeptical of China for historical reasons dating back centuries, the nation has shown a willingness to balance between competing concerns for sovereignty and prosperity. Economically, diplomatically, and militarily, South Korea hedges than many in Washington are willing to acknowledge and is increasingly open to collaborating with China in key areas over the U.S.

Comparatively, relations between China and Japan are fraught with tension and hostility. Following Japan’s defeat in WWII and the end of the Chinese Civil War in 1949, historical issues stemming from atrocities committed by Japanese Imperial forces during the war and previous occupations became one of the most influential and prominent aspects of Chinese relations with Japan. However, after the Sino-Soviet split in the 1960s, the CCP recognized the need to adjust its relationship with Japan (as well as the United States) and move towards a more cooperative stance in order to balance against the Soviet Union.

Japan established formal diplomatic relations with the PRC in 1972, seven years ahead of the United States and 18 years ahead of South Korea. However, relations between the two nations have often run hot due to historical issues and territorial disputes, such as the dispute over the Senkaku Islands (known as the Diaoyu islands in China).[11] The latter dispute caused relations to sour drastically in 2013, with 5.2% of Chinese and 9.6% of Japanese viewing the other country favorably.[12]

Despite diplomatic tensions, trade and economic ties between Japan and China remain strong. Arguments made by the U.S. urging companies to relocate their supply chains away from China have been met with mixed reviews in Japan. Overall, Japan, like South Korea, seeks to hedge its bets when it comes to U.S.-China friction in the economic sphere. However, if forced to choose it is widely assumed that Japan would side with the U.S. over China in most if not all serious confrontations.

U.S. Policy Recommendations

Japan-ROK Historical Resolution

Unresolved historical issues between South Korea and Japan remain the single most detrimental source of conflict in the U.S.-ROK-Japan trilateral security alliance. Multiple issues stemming from Japan’s actions leading up to and during WWII continue to impact the relationship. Such conflict severely hampers the effectiveness of the trilateral security alliance and compromises stability in the region, leaving the door open to adversaries like China, Russia, and North Korea to take advantage.

The U.S. has always served as the binding agent that holds Japan and South Korea together and has often interjected itself as a mediator to force both nations to cooperate on joint security and related matters. Both nations clearly want the U.S. to get involved, even if it’s motivated by a desire to get the Americans to side with them over their rival. The U.S. must commit to working with both South Korea and Japan to fully overcome their historical differences at the high diplomatic and bureaucratic level and transition all three powers into a true trilateral security alliance. Anything less than a forceful and attentive U.S. response will result in the same status quo with a relationship destined for further dysfunction and ineffectiveness.

Transfer of Operational Control (OPCON)

The Administration and Department of Defense must continue to work closely with their South Korean counterparts in order to help them reach the necessary benchmarks to qualify for OPCON no later than 2023. This should be a top priority for the Administration as increased control and sovereignty for South Korea will lead to a more invested and capable security partner and strengthen the overall U.S.-ROK relationship. Conversely, the more this transfer is delayed, the more our relationship will continue to experience friction.

Consensus Over Special Measures Agreement (SMA) Negotiations

Continued disagreement in burden sharing negotiations constitutes a serious threat to USFK readiness against rising threats and will continue to erode goodwill, trust, and respect between our two nations. A fractured US-ROK relationship will only further strengthen the hands of regional adversaries like Russia, China, and North Korea, who will feel increasingly emboldened to use intimidation and coercive measures to extract strategic concessions from South Korea.

Given South Korea’s growing economy, along with continued uncertainty over North Korea’s regional strategy and China’s increasingly aggressive tactics and military buildup, one would conclude that the ROK should shoulder more of the cost of hosting USFK forces. While both sides seem closer to an agreement over burden sharing compared to a year ago, the strategy of the Administration asking for astronomically high increases in ROK spending and pressuring the government publicly is a misinformed strategy doomed to fall on deaf ears given South Korea’s culture and other significant security contributions. Increases in ROK contributions to the burden sharing agreement should come gradually over time instead of all at once, especially in the wake of the economic costs the COVID-19 pandemic has imposed on both of our nations. Both the U.S. and ROK must focus on the mutual necessity of a stable SMA agreement in order to deter existential threats versus the smaller differences that separates them.

Immediate resolution of SMA negotiations is especially important given burden sharing negotiations with Japan are approaching as well. Both partners must come back to the table with serious and realistic proposals that offer the best path forward for security on the Korean peninsula.

Increase U.S.-ROK-Japan Cooperation on North Korea

Countering threats from North Korea continues to be the most unifying issue between Japan and South Korea, despite disagreements between all three on how much emphasis to place on pressure or concessions. While trilateral exercises are unlikely at this point in time, the U.S. should continue to prioritize them as a goal to work towards in order to cement military readiness and trilateral cooperation. Until then, the U.S. should work to focus the attention of Japan and South Korea on the immediate threats North Korea poses and impress upon both nations that their combined survival and prosperity is greater than the historical differences that divide them. In addition, the U.S. should include both the ROK and Japan in larger multilateral exercises that would allow forces to work together alongside other nations while saving face politically.

Great Power Competition Assurances for Japan and South Korea

Great Power Competition between the U.S. and China is a costly but necessary development in the U.S.-China relationship in order to preserve American interests domestically and abroad. However, some of our allies, including the ROK and Japan, maintain a different relationship — and geographical proximity — to China. Neither nation enjoys the rich economic or strategic advantages the U.S. possesses, and both are deeply tied to the Chinese economy and stand to lose a lot more for much less than their American counterparts.

In order to inspire confidence in American leadership and recruit support, the U.S. must offer substantial assurances to its allies in the Indo-Pacific that it will support them in the event they suffer collateral damage from U.S.-China friction. This could take the form of advantageous trade deals, development projects, security commitments, and partner projects between multilateral development finance institutions. In order to show the world and its allies that it’s serious about confronting China head on and committed to ensuring regional prosperity, the U.S. must infuse a large amount of capital into its alliance structures globally in a way that speaks to our partners’ immediate and long-term concerns and purchases their support in confronting China. This investment should begin with our invaluable partners in the Indo-Pacific and Pacific Island nations.

Further, the ROK and Japan should recognize the true aggressor in the region as China has repeatedly abused bilateral diplomatic and economic relationships to extract concessions through economic coercion and military threats. Episodes including China’s harsh punishment of South Korea after its acquisition of the THAAD missile defense system and continued provocations surrounding the Japan-administered Senkaku islands serve as clear indicators for what China’s true intentions are.


[1] The U.S.-Japan Security Treaty of 1951 was negotiated while Japan was still under occupation by American forces and dictates Japan to grant the U.S. territory to establish military facilities while prohibiting Japan from doing the same with any other foreign powers. The Treaty of Mutual Cooperation and Security of 1960 expanded on the 1951 treaty by enacting mutual defense obligations if either nation was ever attacked.

[2] Congressional Research Service. The U.S.-Japan Alliance (RL33740; June 13, 2019), prepared by Emma Chanlett-Avery.

[3] Japan. Constitution of Japan, 1947.

[4] Congressional Research Service. U.S.-South Korea Alliance: Issues for Congress (IF11388; June 23, 2020), prepared by Emma Chanlett-Avery.

[5] The Genron NPO, “The Japan-South Korea Joint Public Opinion Poll 2019,” The Genron NPO and East Asia Institute, July, 2019, https://www.genron-npo.net/en/opinion_polls/archives/5489.html.

[6] The Genron NPO, “The Japan-South Korea Joint Public Opinion Poll 2019,” The Genron NPO and East Asia Institute, July, 2019, https://www.genron-npo.net/en/opinion_polls/archives/5489.html.

[7] “South Korea’s ‘Three No’s’ Announcement Key to Restoring Relations with China.” The Hankyoreh, 2 Nov. 2017, english.hani.co.kr/arti/english_edition/e_international/817213.html.

[8] The Kuril chain of islands are located off the northeast coast of Hokkaido, Japan’s northernmost island. The Soviets invaded the island chain in 1945 near the end of the war and have maintained control since.

[9] “Publics Worldwide Unfavorable Toward Putin, Russia”. Pew Research Center. October 16, 2017.

[10] Congressional Research Service. South Korea: Background and U.S. Relations (IF10165; April 22, 2020), prepared by Mark E. Manyin, Emma Chanlett-Avery, and Brock R. Williams.

[11] The Senkaku / Diaoyu Islands are a group of uninhabited islands located between the coasts of Okinawa, Taiwan and mainland China. The islands have been under the administrative control of Japan since 1895. The issue of sovereignty over the islands arose during the 1970s when evidence of unexplored oil reserves surfaced. Standoffs between Japanese and Chinese vessels continue to escalate tensions, most notably in 2013 when Japan’s purchase of the islands significantly escalated the risk for conflict in the region.

[12] The Genron NPO, “Why do the Japanese have negative views of China?,” The Genron NPO and East Asia Institute, October 25, 2019, https://www.genron-npo.net/en/issues/archives/5507.html.

Congressman Ted S. Yoho (R-FL), DVM Former Lead Republican on the House Foreign Affairs Subcommittee on Asia, the Pacific, & Nonproliferation.

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