The U.S.-Japan Security Alliance

The U.S.-Japan Security 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, in exchange for maintaining a large military presence in the country.
  • 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 foreign country.
  • The allies have recently grappled with how to deal with a nuclear North Korea and a more assertive China. They have also quarreled over U.S. military bases and cost-sharing.


Forged in the wake of World War II, the U.S.-Japan security alliance is as important as ever to both countries’ interests in Asia. In recent years, a more assertive China, a nuclear-armed North Korea, and other challenges have pushed the alliance to make historic adjustments, including crafting a larger role for Japan’s military. 

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Meanwhile, long-running conflicts over issues such as U.S. military bases on Okinawa and cost-sharing continue to rankle the partnership. The Donald Trump administration escalated the dispute over Japan’s financial contributions to the alliance, publicly accusing Tokyo of not paying enough to house U.S. troops, but President Joe Biden has so far downplayed tensions in the relationship.

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.

At the time, the United States was keen on using the alliance to bolster its strategic presence in East Asia. It faced a divided Korean Peninsula in the wake of the Korean War and a Cold War climate in which the Chinese and Soviet militaries were expanding their breadth and capabilities. Against this security backdrop, Yoshida’s government created the Self-Defense Force (SDF) in 1954, despite strong domestic objections based on Article Nine of the postwar constitution, which eschews the maintenance of military forces or the use of those forces to settle international disputes.

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 foothold in Asia. Years later, the United States sparked protest in Japan by using the bases to support combat operations during the Vietnam War.

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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 1970s, as the United States withdrew from Vietnam, Japan began to carve out a larger role within the alliance. It issued its first postwar defense strategy and began clarifying how it would partner with the U.S. military. The two allies undertook studies on interoperability and launched joint training and exercises.

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The 1990–91 Gulf War spurred debate in Japan about whether its constitution allowed the SDF to join the U.S.-led coalition to expel Iraq from Kuwait, a force that had been authorized by the UN Security Council. Ultimately, Japan contributed funds but did not send troops. Japanese military officers and government officials later said they were humiliated by their lack of participation in the war and resolved to change the country’s pacifist constitution. In 1992, a new law stipulated the conditions for SDF deployment in UN peacekeeping operations, and the following year, the first SDF unit was sent abroad to Cambodia.

The fall of the Soviet Union prompted the allies to adopt new guidelines [PDF] in 1997 that expanded where Japan’s military could operate, from its home islands to “surrounding areas.” Some perceived the move as Japan taking greater responsibility for its own defense.

The early 2000s marked a period of increased defense cooperation. In November 2001, the government of 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 Shinzo Abe, 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.

Since then, the countries have continued to deepen their defense cooperation. Abe’s successors, Yoshihide Suga and Fumio Kishida, who are also members of the Liberal Democratic Party (LDP), have mostly shared Abe’s foreign policy outlook, viewing China’s increasing power with concern and supporting increased defense spending. The United States and Japan have worked closely on developing ballistic-missile technology, with the 2019 U.S. Department of Defense Missile Defense Review describing Japan as one of the United States’ “strongest missile defense partners” [PDF]. In 2020, the United States approved the sale of 105 F-35 fighters to Japan. Meanwhile, Japan has committed to working with the United States to improve space, cyber, and maritime awareness capabilities and deepen science and tech cooperation, focusing on defense applications of unmanned systems and artificial intelligence.

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.

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. Japan claims that North Korea abducted seventeen Japanese citizens in the 1970s, five of whom were eventually returned to Japan, while the others are still missing. 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.

The Trump administration’s efforts to engage Kim in direct diplomacy sparked fears in Tokyo that Japan’s interests would be disregarded in any deal. But by 2021, talks on North Korea’s denuclearization had stalled, with North Korea restarting its nuclear reactor program and resuming missile testing. Rejecting Trump’s unilateral approach, the Biden administration has said it will work “in lockstep” with Japan and South Korea to revive dialogue with North Korea. 

How have the allies grappled with China?

Since the 1996 Taiwan Strait Crisis, during which the United States sent aircraft carriers to the region in response to Chinese missile tests, China’s rapid rise has been a top concern for the alliance. In 2010, it surpassed Japan as the world’s second-largest economy, and its growing defense budget and military modernization have prompted worries about its global ambitions.

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. Intermittent diplomatic flare-ups, including in 2013 when China announced the creation of an air defense identification zone [PDF] over the contested islands, have led many observers to fear a military clash, especially one that could draw in the United States.

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 to Asia,” which sought to strengthen military and economic ties with partners in the region, including Japan. The 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 during which his fellow leaders agreed to expand cooperation on vaccines, climate change, technology, and supply-chain resilience. 

Despite the importance of Japan’s close economic ties with China, Tokyo remains concerned about China’s military rise and has in recent years angered Beijing by voicing concerns over Chinese maritime actions, human rights in Hong Kong and Xinjiang, and stability in the Taiwan Strait.

Taiwan, in particular, has become increasingly relevant, with Japan’s 2021 defense strategy [PDF] emphasizing for the first time the importance of maintaining stability across the Taiwan Strait for Japan’s security. Biden and Suga released a joint statement expressing concern over Chinese behavior towards Taiwan, and Japanese defense officials have called for Japan to defend Taiwan in the event of war. In March 2021, the U.S. defense secretary and Japan’s defense minister agreed that Washington and Tokyo would cooperate closely in any such conflict.

Why is Okinawa one of the most contentious issues?

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. Continued construction delays and ballooning costs have complicated the project and put the relocation in doubt.

Who contributes more to the alliance?

Cost-sharing between allies has been a fraught issue in the wake of the Trump administration’s push for Japan and other countries to contribute more. 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 ranges from $1.7 billion to $2.1 billion per year, according to a 2019 report [PDF] by the Congressional Research Service. The United States spends $1.9–2.5 billion per year on base operation, 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 factored into the balance sheet.

After Trump pressed Tokyo to quadruple its payments, Biden has attempted to de-escalate the situation. While negotiations for a new, five-year contract are still underway, the Biden administration agreed to extend the current arrangement with Japan for another year, during which Tokyo will spend $1.9 billion.

Experts note that the United States enjoys significant strategic benefits from the bases, such as the ability to deter aggression from China and North Korea, as well as cost savings by having its military forward deployed in Japan.  

Many analysts believe the alliance has become more balanced as Japan has boosted its defense capabilities and integrated more with U.S. forces. The countries’ joint response to the 2011 earthquake and tsunami that struck Japan’s Tohoku region marked the largest bilateral mission in the history of the alliance.

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. The ruling LDP further pledged in October 2021 to double defense spending, to 2 percent of gross domestic product (GDP), though it did not specify a timeframe.

“Despite the challenges facing the alliance, the decades of close partnership has led to a largely common view of security issues in Asia,” says the Hoover Institution’s Michael Auslin. “The threat of both China and North Korea continues to drive Tokyo and Washington closer together in pursuit of shared interests, such as freedom of navigation and aerial overflight, denuclearization, cyber security, and regional cooperation.”

Recommended Resources

CFR’s Sheila A. Smith unpacks the debate in Japan over constitutional revision.

Smith explains how Japan is upgrading its military.

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

This Atlantic Council report details how emerging technologies could shape the U.S.-Japan alliance

For Foreign Affairs, Akira Igata and Brad Glosserman discuss Japan’s important role in addressing economic security challenges in the Indo-Pacific.

Beina Xu contributed to this Backgrounder. 

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

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