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.…