Over the last ten years, Japan has shed its pacifist identity. After promising, post–World War II, to maintain only a tiny military, Tokyo is now building up truly capable armed forces and a sizable defense industrial base. In December 2018, for example, the country announced plans to modify its Izumo-class destroyers so they could operate F-35B fighters—effectively giving Japan its first aircraft carrier since 1945—and to buy 147 F-35 fighter jets. In 2023, it allowed its companies to start selling certain offensive weapons and weapons parts. And last month, Tokyo scrapped most of the remaining limits on arms exports, including destroyers, missiles, and jets.

Japan’s pivot should be widely welcomed in Washington, which has long sought to get its wealthy East Asian ally to spend more on defense. These moves are designed to strengthen the alliance, as Japanese officials remain deeply committed to their partnership with their U.S. peers. A stronger Japan, for example, could be critical in deterring China from attacking Taiwan. Beijing is less likely to confront a coalition that features not just U.S. and Taiwanese forces but well-equipped Japanese ones, as well. And increasingly, China has to assume that Tokyo would enter a conflict over the island, meaning that any Taiwan war would involve Japanese bases, missiles, sensors, air defenses, and logistics networks, making a quick victory hard to achieve.

Still, whether Tokyo’s efforts actually end up strengthening the U.S.-Japanese partnership is an open question—and the answer is highly contingent on how Washington reacts. Ever since U.S. President Donald Trump returned to office in 2025, the United States has been casting U.S. alliances in transactional terms, the Japanese one among them. In April 2025, for instance, Trump slapped 25 percent tariffs on Japanese goods. (The two sides eventually struck a deal setting most rates to 15 percent, before the Supreme Court ruled the tariffs impermissible.) Trump also previously demanded that Japan pay roughly four times as much to the United States in exchange for continuing to host U.S. troops. He called Japan “spoiled” for “having ripped us off for 30, 40 years.” If the United States continues to lambast Japan, then Tokyo indeed might forge a more independent path. Its increased defense spending and growing strength, after all, act as an insurance policy that helps keep Japan safe in the event the United States wavers.

Washington, then, should abandon its efforts to extract as much as it can from Japanese coffers. It must instead look for ways to capitalize on Tokyo’s strength—such as by working together on military production, or better connecting their command chains in the Pacific. This might make some U.S. officials, accustomed to being by far the more powerful partner, wary. But any loss of American dominance is well worth the benefits. For years, the United States has been searching for a way to better constrain Beijing. A Japan that can hold the line early in a crisis and help the United States fight back is an excellent solution.

Japan has long toyed with the idea of shedding its pacifist posture, but its security evolution only began in earnest in 2015. That year, Japanese Prime Minister Shinzo Abe passed legislation that permitted Japan’s Self-Defense Forces to use force in limited cases of what it called “collective self-defense,” such as if an attack on the United States threatened Japan’s survival. (Previously, Japan allowed the use of force only when Japan itself was attacked.) The reform was hugely controversial at the time of passage, prompting outrage and protests. But it went into effect, and Japan has further loosened the constraints on its military in the time since. In 2017, for example, Abe signaled that Tokyo would no longer treat its informal one-percent-of-GDP ceiling on defense spending as inviolable. In 2018, Japan created the Amphibious Rapid Deployment Brigade, a marine-style unit designed to defend and retake remote islands. And Japan's 2022 National Security Strategy and Defense Buildup Program committed the country to acquiring counterstrike capabilities, including longer-range missiles.

No one seems more committed to this shift than Japan’s current prime minister, Sanae Takaichi. An Abe protégé, Takaichi took office........

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