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, but new challenges from China, North Korea, and within the alliance itself raise questions about its future.
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 has 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. Meanwhile, internal conflicts over issues such as U.S. military bases on Okinawa and cost-sharing have cast doubts over the long-running partnership.

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.

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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.

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.

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A bar chart shows that more U.S. service members are deployed in Japan than any other country.

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.

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.

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The fall of the Soviet Union prompted the allies to adopt new guidelines 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. The two have also continued to work closely on developing ballistic-missile technology, with a 2019 U.S. Department of Defense report describing Japan as one of the United States’ “strongest missile defense partners” [PDF].

“Abe’s efforts to boost Japan’s defense budget and revise its constitution not only show that his country is willing to do more in the alliance,” says Yuki Tatsumi, director of the Stimson Center’s Japan Program, “but it also makes Japan stronger on its own.”

How does North Korea factor into the alliance?

The threat from North Korea, which Japan has called its “most serious and pressing,” has exposed limitations [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, including Abe, have refused talks with North Korea until the issue is resolved, though in 2019 Abe said he was considering a summit with leader Kim Jong-un.

Meanwhile, recent efforts by U.S. President Donald J. Trump and South Korean President Moon Jae-in to restart a dialogue with North Korea on denuclearization, including historic summits with Kim, have roused fears in Tokyo that Japan’s interests may not be served in any grand bargain. Some worry that Washington could accept a deal that protects the U.S. mainland but stops short of removing North Korea’s capacity to strike Japan.

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.

In 2011, U.S. President Barack Obama’s administration announced a major strategic shift—the “pivot” or “rebalance” to Asia—intended to strengthen military and economic ties with partners in the region, including Japan. The move was widely seen as a response to China’s growing regional influence, but some experts say it did not do enough to curb Beijing’s assertiveness.

A bar chart shows that the United States spends more than China and Japan on military expenditure as a percentage of GDP.

The Trump administration has a made similar strategic adjustment with its Free and Open Indo-Pacific strategy, which analysts say is an acknowledgement of and response to China’s ambitions. The strategy includes maintaining peace and the rule of law, reinforcing freedom of navigation at sea, respecting national sovereignty, and protecting open markets. Japan and the United States affirmed their commitment to these principles in an April 2019 joint statement [PDF]. The United States has also pushed for the revival of a security arrangement with Australia, India, and Japan—the so-called Quad—and authorized $1.5 billion annually for programs in Asia. The United States and Japan have also launched negotiations for a free trade agreement.

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, but recent administrations have considered them to be administered by Japan and thus covered by the 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.

Despite lingering tensions, relations between Japan and China have stabilized in recent years. In late 2018, Abe traveled to Beijing for a state visit with President Xi Jinping, the first of its kind since 2011. That same year, the countries established a military hotline to avoid maritime accidents and agreed to hold regular meetings between defense officials.

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-four thousand 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 in 1995 by U.S. service members galvanized eighty-five thousand residents to protest. Other allegations of sexual violence by U.S. military personnel surfaced in 2008 and 2012.

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. Abe, however, has insisted that the relocation happen soon, and some Marines could be transferred in the next few years.

Who pays for the alliance?

Trump has called for allies around the world to shoulder more of the costs of partnerships with the United States, and Japan is no exception. As a presidential candidate in 2016, Trump complained that Japan did not pay enough for hosting U.S. bases. In recent months, he has renewed calls for changes to the alliance, which he described as “unfair.”

Determining how much Japan and the United States spend on the alliance is complicated, and there is no widely accepted balance sheet. Japan’s defense minister said in 2017 that Japan paid 86 percent of the total cost, though media outlets have estimated the number to be between 40 and 50 percent. Japan is responsible for providing 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 approximately $2 billion per year on the bases.

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, Japanese lawmakers approved a $47 billion defense budget, the country’s largest in years and one that included plans to purchase advanced weapons from the United States. The budget is part of a plan to increase defense spending to $240 billion by 2023.

“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.

In her 2019 book, Japan Rearmed, Smith discusses how Japan is changing its approach to military power.

This 2019 report [PDF] from the Congressional Research Service analyzes the U.S.-Japan alliance.

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

Journalist Kevin Knodell argues in Foreign Policy that joint military exercises are crucial to strengthening the U.S.-Japan alliance.

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

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