The U.S.-Japan Alliance

The U.S.-Japan Alliance

The alliance with Japan has been the cornerstone of U.S. security policy in East Asia for decades. Now, Japan’s role in global security is growing as challenges from China and North Korea mount.  
Former U.S. Defense Secretary Leon Panetta addresses U.S. and Japanese forces.
Former U.S. Defense Secretary Leon Panetta addresses U.S. and Japanese forces. Yuriko Nakao/Reuters
  • The alliance began during the U.S. occupation after World War II. The United States pledged to defend Japan, which adopted a pacifist constitution. Recently, however, Japan has stepped up its contributions to the alliance.
  • There are more than eighty U.S. military facilities in Japan. More U.S. service members are permanently stationed in Japan than in any other country.
  • The allies have grappled with how to deal with a more assertive China and a nuclear North Korea. In recent years, Tokyo and Washington have deepened their security cooperation in the Indo-Pacific.


Forged in the wake of World War II, the U.S.-Japan alliance is as important as ever to both countries’ interests in Asia. A more assertive China, a nuclear-armed North Korea, and a revisionist Russia that is waging a war on Ukraine have pushed the alliance to make historic adjustments, including crafting a larger role for Japan’s military. In 2022 Japan announced a new military and defense strategy, pledged to nearly double its military spending and acquire long-range counterstrike capabilities, and introduced major reforms to the Japan Self-Defense Forces, as its military is officially known. Meanwhile, some sticking points in the partnership remain, such as cost-sharing and U.S. military bases on Okinawa.

How did Japan and the United States become allies?

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Signed in 1951 alongside the Treaty of San Francisco that formally ended World War II, the U.S.-Japan Mutual Security Treaty was a ten-year, renewable agreement that outlined how Japan, in light of its pacifist constitution, would allow U.S. forces to remain on its soil after Japan regained sovereignty. This early pact dovetailed with the Yoshida Doctrine—a postwar strategy crafted by Prime Minister Shigeru Yoshida that saw Japan rely on the United States for its security needs so the country could focus on rebuilding its economy. Yoshida’s government created the Self-Defense Forces (SDF) in 1954, despite strong domestic objections based on Article Nine of the postwar constitution, which prohibits the maintenance of military forces or the use of those forces to settle international disputes.

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In 1960, the U.S.-Japan agreement was revised, granting the United States the right to establish bases on the archipelago in exchange for a commitment to defend Japan in the event of an attack. The bases gave the U.S. military its first permanent presence in Asia. Years later, the United States sparked protests in Japan by using the bases to support combat operations during the Vietnam War.

In 1967, Prime Minister Eisaku Sato established the Three Non-Nuclear Principles—no possession, production, or introduction—in part to allay concerns that the nuclear arms on U.S. bases in Japan would expose the country to attacks. Since then, Japan has relied on the U.S. nuclear umbrella to deter potential aggressors.

How has the alliance changed?

In the latter part of the twentieth century, Japan began to carve out a larger role within the bilateral relationship. In 1992, a year after the Gulf War, the Japanese government passed a new law stipulating for the first time the conditions for SDF deployment in UN peacekeeping operations. The first SDF unit was sent abroad to Cambodia the following year. 

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The early 2000s marked a period of increased defense cooperation between the United States and Japan. In November 2001, the government of Japanese Prime Minister Junichiro Koizumi dispatched the Maritime Self-Defense Force to the Indian Ocean to provide logistical support for U.S. military operations in Afghanistan, marking Japan’s first overseas military action during a combat operation. In 2003, it sent forces to aid in Iraq’s postwar reconstruction efforts.

In 2015, under Prime Minister Abe Shinzo, Japan reinterpreted its constitution in a historic move that allowed its military to defend allies for the first time, but under limited circumstances. The change helped pave the way for the United States and Japan to revise their defense guidelines once again, expanding the scope of their military cooperation and focusing the alliance on current threats—including from China and North Korea—and new technologies.

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Abe’s successors, Suga Yoshihide and Kishida Fumio, who are also members of the Liberal Democratic Party (LDP), have mostly shared Abe’s foreign policy outlook, viewing China’s increasing power “as a matter of serious concern” [PDF] and supporting increased defense spending and enhanced security cooperation with the United States. Washington and Tokyo have worked closely on developing ballistic-missile technology and are now collaborating on improving space, cyber, and maritime awareness capabilities; deepening science and tech cooperation, focusing on defense applications of unmanned systems and artificial intelligence; and collaborating on licensing, developing, and producing missiles as well as building and repairing U.S. navy ships and aircrafts in Japan.

Russia’s war in Ukraine presented another turning point in Japan’s strategic outlook and foreign policy approach. Kishida has linked the ongoing war in Ukraine to security in the Indo-Pacific, becoming Japan’s first postwar leader to enter a war zone when he visited Kyiv in early 2023. In his April 2024 address to a joint session of the U.S. Congress, Kishida warned that the “Ukraine of today may be East Asia of tomorrow.” Since the start of the war in 2022, Japan has pledged more than $10 billion in financial and humanitarian aid to Ukraine. In the early period of the invasion, the country also supplied non-lethal military vehicles and equipment [PDF], such as drones, bulletproof vests, and winter battle uniforms to Ukrainian soldiers. Analysts say this commitment represents a significant military upgrade given Japan’s history of stringent defense equipment export controls.

In December 2022, Japan issued three documents that detail the country’s new national security and defense strategy. Among other provisions, the plan aims to grow its defense spending over the next five years, establish a Joint Operations Center (J-JOC) that will improve the SDF’s operational effectiveness during a potential conflict, and acquire long-range counterstrike capabilities. According to the new strategy, these upgraded defense capabilities will “further enhance deterrence and response capabilities” of the U.S.-Japan alliance.

Kishida’s state visit to Washington in April 2024 further reinforced the two countries’ partnership. Calling each other “global partners” in their joint statement, U.S. President Joe Biden and Kishida produced more than seventy agreements during the state visit. Strengthening defense and security cooperation topped their agenda, including deepening ties between their defense industries and working together on training and maintenance of equipment.

The alliance has also extended to addressing nonmilitary threats, including climate change. In April 2021, President Biden and Prime Minister Suga announced a climate partnership [PDF], agreeing to boost cooperation on green technologies and coordinate on promoting decarbonized infrastructure and capacity-building in developing countries in the Indo-Pacific. Experts say that the partnership in part spurred Japan’s announcement that same month of a more ambitious emissions-reduction commitment. Economic and technological cooperation has also become more integrated. The United States’ 2022 “Chip 4 Alliance” proposal aims to restructure the global semiconductor supply chain with Japan, South Korea, and Taiwan at the center, and the United States and Japan plan to improve commercial information communication technology.

How have the allies grappled with China?

China’s increasing assertiveness and its global ambitions have prompted concerns within the U.S.-Japan alliance. At the heart of tensions between China and Japan is a long-standing territorial dispute over the Senkaku/Diaoyu Islands, a cluster of uninhabited islets in the East China Sea. Washington has maintained a neutral stance on the islands’ sovereignty. However, since the Obama administration, the United States has considered the islands to be administered by Japan and thus covered by the U.S.-Japan security treaty. 

In response to China’s increased assertiveness, recent U.S. administrations have shifted strategic focus to the Indo-Pacific, beginning with Obama’s 2011 pivot or rebalance to Asia, which sought to strengthen ties with partners in the region, including Japan. The Donald Trump administration revived the Quad, a security arrangement among the United States, Australia, India, and Japan, over concerns about China’s behavior. Biden further committed to the Quad, convening meetings where the leaders agreed to expand cooperation on vaccines, climate change, technology, and supply-chain resilience. According to Japan’s 2022 updated national security strategy, the U.S.-Japan alliance is at the center of promoting Japan’s Free and Open Indo-Pacific initiative, a set of principles for peace, prosperity, and security in the region.

Despite the importance of Japan’s close economic ties with China, Japan’s new national security strategy labels China as an “unprecedented strategic challenge.” Furthermore, Tokyo has in recent years angered Beijing by voicing concerns on human rights in Hong Kong and Xinjiang, Chinese maritime actions, and stability in the Taiwan Strait

Taiwan in particular has become the subject of increasing focus in Tokyo, located just 68 miles (110 kilometers) from Yonaguni Island, the westernmost point of Japan. In 2021, former Prime Minister Abe declared that “a Taiwan emergency is a Japanese emergency,” and therefore, also an emergency for the U.S.-Japan alliance. Japan’s defense strategy [PDF] that same year emphasized for the first time the importance of maintaining stability across the Taiwan Strait for Japan’s security, and Japanese defense officials have called for the country to defend Taiwan in the event of war.

A major turning point in Japan’s approach to Taiwan came when China fired missiles that landed in Japan’s exclusive economic zone (EEZ) after then U.S. Speaker of the House Nancy Pelosi visited Taiwan in 2022. Over the past decade, Japan has built military bases on its southwestern islands, which could prove critical during a “Taiwan contingency” given their proximity, particularly Yonaguni (established in 2016), Miyako (2019), and most recently, Ishigaki (2023). Recent reports suggest Japan plans to increase its military personnel, expand the existing bases for training, and deploy military equipment to the islands in preparation of a possible conflict in the Taiwan Strait.

Japan's Prime Minister Kishida visits Philippines
Japan’s Prime Minister Fumio Kishida visits the BRP Teresa Magbanua ship at the Philippine Coast Guard headquarters in Manila, Philippines in November 2023. Ezra Acayan/REUTERS

In 2023, the United States conducted a joint military exercise with Japan on Ishigaki. Meanwhile, the partners have also held military drills with allies in the South China Sea. In April 2024, the United States, Australia, Japan, and the Philippines conducted joint naval drills in the Philippines's EEZ ahead of a U.S.-Japan-Philippines trilateral summit in Washington. There are also reports that the United States, Japan, and the Philippines plan to launch joint naval patrols in the South China Sea later in the year.

How does North Korea factor into the alliance?

The threat from North Korea, which Japan has called [PDF] “grave and imminent,” became a major focus [PDF] in the alliance dating back to the mid-1990s, when North Korea fired a ballistic missile into the Sea of Japan and withdrew from the Nuclear Nonproliferation Treaty. The alliance’s 1997 framework intended to, among other things, improve Japan’s preparations for a crisis on the Korean Peninsula.

Tokyo and Washington started working more closely on missile defense after North Korea fired another missile over Japan in 1998. Since then, North Korea has launched dozens of missiles over Japan and claims it can mass-produce medium-range missiles. The intensifying threat has led some in Japan to push for acquiring nuclear weapons for self-defense and missiles for preemptive strikes.

Tokyo’s willingness to pursue diplomacy with Pyongyang has been complicated for years by a lingering controversy. In the 1970s, North Korea abducted seventeen Japanese citizens, five of whom were eventually returned to Japan, while the others are still missing. (North Korea denies that these individuals were abducted). Japanese leaders had long refused talks with North Korea until the issue was resolved; Abe and Suga both expressed willingness to meet with North Korean leader Kim Jong Un, though neither ever did. While Kishida has said he is willing to arrange a summit with Kim, the North Korean leader’s demands that Japan tolerate Pyongyang’s weapons development and ignore the abductions have resulted in nonstarters. U.S. officials have said Washington would welcome high-level engagement between Tokyo and Pyongyang “without preconditions.” 

The rising threat of North Korea’s missile development has also caused Japan and South Korea to partially set aside deep historical issues and pursue trilateral cooperation with the United States. Following the trilateral meetings at the 2023 Camp David Summit and the 2022 Phnom Penh Summit, the three countries have committed to share real-time North Korean missile warning data and establish a multiyear trilateral exercise plan.

Why is Okinawa a contentious issues in the alliance?

For decades, U.S. Marines have been stationed in Okinawa Prefecture, which hosts a majority of the approximately fifty-five thousand [PDF] U.S. military personnel in Japan. Thirty-one of the eighty-five U.S. military facilities in Japan are on Okinawa, despite it being the poorest and among the smallest of Japan’s prefectures.

Two people look out from a balcony down on the Futenma air base.
Two people look toward the Futenma air base in Okinawa. Carl Court/Getty Images

Many Okinawans resent military activity in the prefecture, which was the site of one of the bloodiest battles between Japanese and U.S. forces during World War II. An estimated 40,000 to 150,000 Okinawan citizens were killed. Today, one of the biggest magnets for local criticism is the U.S. Marine Corps Futenma air base, which is located near schools and hospitals. While the base provides some economic benefits, such as jobs, residents have repeatedly voiced concerns about accidents and violent crime. 

The gang rape of a twelve-year-old girl by U.S. service members in 1995 galvanized eighty-five thousand residents to protest, and sexual violence and misconduct by U.S. service members remains a problem. Recently disclosed investigations by the U.S. Navy recorded eight instances of sexual offenses between 2017 and 2019; publicly available Marine Corps court-martial records reveal sixty-nine convictions of U.S. marines in Okinawa involving sexual wrongdoing toward minors between 2015 and 2020. 

In a bid to ease tensions, the United States and Japan agreed in 2006 to relocate Futenma to a less populated area on Okinawa and transfer eight thousand Marines to Guam. But the agreement has yet to be realized. Many residents and local officials oppose keeping the base on Okinawa, voting in early 2019 against the relocation plan. Land reclamation for the facility relocation began in early 2024 despite residents’ concerns over the cost and Okinawa’s potential involvement in a Taiwan contingency. Other polling on the base relocation, however, found that some younger Okinawans hold slightly warmer attitudes toward U.S. bases as Japan plans for a more assertive China.

What has each country brought to the alliance?

Cost-sharing has been a fraught issue in the wake of the Trump administration’s push for Japan and other U.S. allies to contribute more funding. Japan provides host-nation support to the United States—the land, labor, and utilities for stationing U.S. forces throughout the country—the cost of which is roughly $2 billion per year. The United States spends $1.9–2.5 billion per year on base operations, military construction, and housing costs in Japan. However, the actual share that the United States and Japan each spend on the alliance is contested; it varies depending on what costs are included in the balance sheet.

After Trump pressed Tokyo to quadruple its payments, Biden has attempted to de-escalate the situation. In 2021, the Biden administration agreed to extend the previous arrangement with Japan for another year, during which Tokyo spent $1.9 billion. But the countries reached an agreement in March 2022 that Japan would pay more than $8.6 billion—around a 5 percent increase from its previous contribution—to host U.S. forces in the country through 2027.

In a sign of Japan taking on a larger security role in the world, the SDF opened its first permanent overseas base in Djibouti in 2011, and announced expansion plans after China opened a base there in 2017. In 2018, Tokyo announced a five-year plan to spend a total of $240 billion on defense, a record amount. It includes plans to purchase advanced weapons from the United States and invest in unmanned systems and other emerging technologies. In 2023, the ruling LDP introduced a new plan to increase the total defense spending to $321 billion by 2027.  At the end of that year, the Japanese cabinet approved a 16 percent increase in military spending for 2024 and eased its ban on lethal weapons exports. Moreover, Japan has expanded its military cooperation with Australia, India, and Southeast Asian countries over the past decade with the goal of creating a lattice of mutually reinforcing relationships in the Indo-Pacific.

Recommended Resources

CFR Senior Fellow Sheila A. Smith unpacks the debate in Japan over constitutional revision in this CFR infoguide.

CFR Fellow David Sacks explains how the U.S.-Japan alliance would be critical for defending Taiwan and examines how the alliance can increase deterrence in the Taiwan Strait or respond if deterrence fails.  

On The President’s Inbox podcast, Smith discusses Japan’s new defense strategy and its decision to double military spending. 

The George Washington University Library lays out the issues regarding the U.S. military presence on Okinawa.

For Foreign Affairs, Senior Political Scientist at the RAND Corporation Jeffrey W. Hornung discusses the importance of elevating the U.S. alliance with Japan.

This 2024 Congressional Research Service report provides an overview of the current issues facing U.S.-Japan relations.

Beina Xu, Lindsay Maizland, Nathanael Cheng, and Clara Fong contributed to this report.

For media inquiries on this topic, please reach out to [email protected].

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