Japan’s prime minister, Fumio Kishida, has pledged to modernise his country’s military alongside US president Joe Biden, warning that Russia’s invasion of Ukraine had opened a dangerous new era and could embolden China. Welcoming Kishida at the White House, Biden hailed the Japanese government’s announcement last month that it will double defence spending over the next five years and develop new capabilities. “Let me be crystal clear: the United States is fully, thoroughly, completely committed to the alliance and more importantly to Japan’s defence,” Biden said. Japan has been officially pacifist since its defeat in the second world war but has been shedding past sensitivities as China rapidly expands its military and North Korea relentlessly tests missiles. In a speech after his White House meeting, Kishida cast his defence strategy as a historic turning point in the US-Japan alliance in the same league as the mutual defence treaty of 1960. “Russia’s aggression against Ukraine has marked the complete end of the post-cold war world,” Kishida said at Johns Hopkins University’s School of Advanced International Studies. “If we let this unilateral change in the status quo by force go unchallenged, it will happen elsewhere in the world, including Asia,” Kishida said, in likely a veiled allusion to fears of a Chinese invasion of Taiwan. The relationship with China, Kishida said, “is the most critical challenge for both Japan and the United States”. Japan has joined western powers in imposing sanctions on Russia and has provided humanitarian, although not military, aid to Ukraine since President Vladimir Putin invaded in February 2022. Kishida called it a “major shift” in Japan’s policy toward Russia after marathon but unsuccessful talks to resolve a dispute over islands seized by Soviet troops shortly after Tokyo’s surrender in 1945. Kishida was visiting Washington at the end of a tour of G7 nations as Japan starts its year leading the elite club of industrial democracies, in which the country is proud to be the only non-western member. “Japan’s participation in the measures against Russia transformed the fight against Russia’s aggression against Ukraine from a transatlantic one to a global one,” Kishida said. Biden hailed Japan’s firmness on Ukraine in the Oval Office meeting. “We’re stepping up to hold Putin accountable for his unprovoked war in Ukraine and I want to thank you, thank you for your strong leadership on this from the first conversation,” Biden said. As part of its new defence policy, Japan is hoping to buy hundreds of Tomahawk cruise missiles, which currently are only in the arsenals of the US and Britain. Japan will also for the first time develop a “counter-strike” capability to hit launch sites for missiles that threaten it. In talks this week between the Japanese foreign and defence ministers and their US counterparts, the two countries also agreed that attacks in space could invoke their mutual defence treaty amid rapid Chinese work on satellites. “Our security alliance has never been stronger,” said a joint statement by Biden and Kishida. “The two leaders reaffirmed that the alliance remains the cornerstone of peace, security and prosperity of the Indo-Pacific.” They also renewed a call to maintain “peace and stability” in the Taiwan Strait. China under President Xi Jinping has been increasingly forceful on Taiwan and staged major military exercises in August after a defiant visit to the self-governing democracy by Nancy Pelosi, then the speaker of the US House of Representatives. Japan is also planning to enter joint exercises with the US and Australia and has coordinated diplomacy as part of the four-way “Quad” that also includes India.