NAGASAKI, Japan—As a teacher, Michiko Yagi told schoolchildren that Japan had made a solemn promise to the world never to wage war again.
Now 87, Yagi had been lucky to survive the atomic blast that obliterated her hometown when she was 6 years old. The 1945 bombing of Nagasaki, and Hiroshima before it, brought an end to Imperial Japan’s brutal march across Asia and turned generations of Japanese against the militarism that led their country to ruin.
Yagi said she felt a sense of pride and safety in the idea, enshrined in Japan’s pacifist postwar constitution, that her nation should never resort to force to settle international disputes or possess a fully fledged military.
“For us, being a pacifist country wasn’t just a political label. It has been our moral compass after the tragedy,” said Yagi.
Today, Japan’s decadeslong embrace of pacifism is fading as the country confronts a more dangerous and unpredictable world.
Wary of China’s expanding military power and anxious over U.S. commitments to protect its allies in Asia, more Japanese say defense spending should be increased to safeguard their country and deter aggression in the region that surrounds it.
Prime Minister Sanae Takaichi, who won a landslide victory in an election in February, is in the vanguard of this shift. A longtime security hawk, she has big plans to beef up Japan’s armed forces with new weapons and capabilities.
She wants to unshackle a defense industry that is stunted, as she sees it, by heavy restrictions on what it can sell overseas. She wants Japan to have its own clandestine intelligence service and is planning a major review of Japan’s national-security strategy to better confront what officials describe as the most fraught security environment modern Japan has faced.
Takaichi even has plans to try to revise the postwar constitution itself, a longstanding goal of her ruling Liberal Democratic Party that has eluded every party leader before her. Changing the constitution could make it easier for future Japanese governments to send troops or ships overseas, as President Trump has called on allies to do in Iran. Japan has so far demurred, citing legal obstacles to venturing into a war zone.
“Times have changed,” Takaichi said in a recent debate in the Japanese parliament, during which opposition lawmakers invoked speeches made 50 years ago to challenge her plans to boost arms exports, a key component of her defense strategy. “The situation surrounding Japan is now extremely severe.”
For the U.S., Takaichi’s plans are entirely in sync with American ambitions to get allies to shoulder more of the burden of their own defense.
The principal U.S. goals in Asia are to maintain military primacy in the Pacific and deter China from moving on Taiwan, a self-ruled island democracy that Beijing views as Chinese territory, to be taken by force if necessary.
Japan plays a critical role: It hosts major American bases and has been steadily fortifying its southwestern flank, a chain of islands stretching from Okinawa to Yonaguni, some 70 miles from Taiwan. Japan has installed missiles, radar, garrisons and electronic-warfare systems on the islands to protect the archipelago amid intensifying Chinese military activity in the East China Sea and—potentially—play a role in any defense of Taiwan.
The buildup is a reaction to increasing Chinese activity in the region. Chinese warplanes skirting Japanese airspace and Chinese ships sailing close to Japan’s territorial waters have become commonplace occurrences, an almost daily reminder to the Japanese of their larger neighbor’s growing military might.
Beijing in recent months has engaged in a campaign of economic coercion against Japan, angered by Takaichi’s November remark that Japan could get dragged into any conflict over Taiwan. Measures have included throttling tourist flights to Japan and pinching Japanese firms’ access to rare-earth minerals and magnets essential for manufacturing.
Beijing has also accused Takaichi of seeking to rekindle Japanese militarism. Analysts say Beijing’s reaction underlines China’s alarm at the prospect of its wartime enemy and close U.S. ally building up its defensive strength.
With the security environment darkening, a 2025 poll by the Japan Press Research Institute found 54% of those polled agreed with the need for greater defense spending. A separate poll last year by the Sankei Shimbun, a conservative daily newspaper, put support for more defense spending at 62%.
Among those in favor, support was highest among younger cohorts, the poll found, with a majority opposed only in those aged over 70.
“It’s absurd to expect the Americans to come to our aid when our own people aren’t even defending our own country,” said Masashi Kajiyama, who is in his 60s and lives in Nagasaki. He said he supports Takaichi’s plans to lift spending on defense and revise the constitution, which he sees as having been imposed on Japan during the U.S. occupation after 1945. With China boosting military spending, Japan needs to do more “before it’s too late,” he said, adding Japan can’t rely on the U.S. to defend it.
For Kazuma Kakehashi, higher defense spending is about deterrence. “Tell them Japan is capable of defending itself,” said Kakehashi, who is in his 20s and works for a company in Osaka. He said he isn’t keen on revising the constitution, however, believing it would risk weakening Japan’s commitment to military action only in self-defense.
In rewriting Japan’s national-security strategy, Takaichi will have to contend with challenges including Japan’s aging population and recruitment shortfalls. Many in Japan retain a suspicion of military authority and some worry that arming Japan risks making the country more of a target.
“As someone that was born in Nagasaki, I’m against all wars,” said Asumi Hidaka, 36, a mother of two young children.
Takaichi has detailed plans for almost $60 billion in new defense outlays in the coming fiscal year, after hitting a target of spending 2% of gross domestic product on defense two years ahead of schedule.
Among other priorities, the country is developing drone-based air and sea defense systems and hypersonic glide weapons that can evade enemy missiles and strike back at targets deep within mainland Asia.
The U.S. under Trump is pushing allies to spend an even greater share of national income on defense, arguing for 3.5% of GDP at least. Trump has berated European allies in particular for relying too much on America’s security umbrella and neglecting their own armies.
Some voters in Japan wonder where the money will come from to lift defense spending further, or if spending on missiles and troops is a wise choice when households are grappling with rising prices.
“I’d rather see an increase in my salary,” said Tatsuo Nakashima, a company employee and Nagasaki native, when asked about higher defense spending.
Still, for many Japanese, strictly adhering to the country’s postwar pacifism when the world seems to be growing more unstable doesn’t seem a wise choice. Russia’s invasion of Ukraine was a shock to Japan, said Akihisa Nagashima, who advised former Prime Minister Shigeru Ishiba on national security.
“We have enjoyed 80 years of peace,” Nagashima said. Now, he said, “people really understand what we need to do.”
Write to Jason Douglas at jason.douglas@wsj.com and Junko Fukutome at junko.fukutome@wsj.com