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When Depopulation Becomes a National Security Risk

March 28, 2025: In 2024, the number of babies born in Japan fell to a record low for the ninth year in a row. With about 1.6 million deaths and 720,988 births, there were about two deaths for every new baby born. Japanese governments have proposed policies to reverse this trend, but they have so far had little success. Thirty percent of the country’s population is over the age of 65, and by 2070, this number is projected to be 40 percent. The shrinking and aging of Japan’s population will transform Japanese society. But it will have a particular effect on a major concern of the government: national defense.

The Japanese government passed a record defense budget in 2024, in line with its commitment to increase its defense spending to two percent of its GDP by 2027. The country’s new prime minister, Shigeru Ishiba, has long sought to bolster Japan’s independent security capabilities and become a more equal partner in its military alliance with the United States, which has for decades pressured Japan to step up. Even before President Donald Trump’s re-election, Japan had begun to make bolder military pledges. Under former Prime Minister Fumio Kishida, who led the country from 2021 to 2024, Japan outlined plans to double its defense spending by 2027, loosen restrictions on weapons development, and strengthen relations with like-minded countries around the world.

The battering of the Liberal Democratic Party in recent national elections has cast doubt on whether these increased investments in defense will be possible. Although the LDP remains the largest party in the National Diet, with Ishiba as its leader, the party lost 56 seats in October 2024, failing to reach a majority. Trump’s determination to put pressure on U.S. allies to pay their “fair share” in maintaining security partnerships has only heightened the stakes.

But even if Ishiba manages to garner the necessary political support for more defense spending, Japan will have to face the dire demographic headwinds. The decline of its population will almost certainly ensure that it will fall short of the grand aspirations of Japanese policymakers and their U.S. counterparts. Japan’s population is so old, and shrinking so quickly, that it may not be able to field and fund an adequate defense force to meet growing alliance demands in an increasingly volatile world. The size of its forces are already vastly outmatched by its primary adversaries; Japan’s military is one-tenth the size of China’s active forces and one-fifth of North Korea’s.

If present population trends continue, they could severely limit recruitment for the already chronically understaffed Japan Self-Defense Force, restrain the state’s ability to tax the population to fund increased defense expenditures, and stifle the innovation needed to compete in the defense sector. Without more people, Japan will struggle not only to address its current security threats but also to play the larger role in global affairs that Japanese and U.S. officials want it to. The solution is at once simple and improbable. People need to have more children, but few leaders are willing to say this out loud or to address the obstacles that younger generations face in balancing their careers with their family lives.

STRENGTH IN NUMBERS

Japan is not the only country suffering from these trends. Several U.S. allies and partners have even lower fertility rates than Japan, facing declines that could soon affect defense preparedness. Ukraine, which had a low birthrate even before Russia’s full-scale invasion in 2022, now has one below one child per woman, according to the UN Population Fund. Taiwan has a fertility rate of around 0.87. (Demographers generally set the “replacement level,” at which a country’s population remains stable, at 2.1 children per woman.) In South Korea, academics and former military professionals have warned that a shrinking population may force an eventual downsizing of its armed forces. And policymakers in the United States will also have to face the reality that the country’s falling birthrates and declining pool of eligible recruits could eventually weaken U.S. forces if such trends continue.

The Japanese military is particularly vulnerable to the consequences of demographic change. Since its founding in 1954, the force has rarely met its recruitment targets, and decades of economic stagnation, stigmas around military service, and recent sexual harassment scandals have discouraged many young Japanese from enlisting. Further, part of the reason Japan needs more troops is that the world is becoming a more dangerous place, and many young people don’t want to put themselves on the frontline. The Ministry of Defense has sought to appeal to younger generations—by using celebrities, messages about peace, and anime in its advertising, for example—and has raised the maximum age of recruits from 26 to 32. But these efforts have had little effect: in 2023, the ministry missed its recruitment goal by more than 50 percent. That failure is not helped by Japan’s ever-dwindling pool of possible recruits. In fact, over the last three decades, the number of Japanese 18- to 26-year-olds, the primary recruiting population, has declined by around 40 percent, from 17.43 million in 1994 to 10.2 million in 2024. To meet its recruitment quotas for the coming decade, Japan would need to eventually enlist more than one percent of its entire population—a herculean task.

The effects of dwindling numbers are already being felt across the ranks. In 2018, Noboru Yamaguchi, a retired lieutenant general in Japan’s army, told me that the warped ratio between senior and junior noncommissioned officers, with many senior officers having only a few junior officers to supervise, has hindered leadership development in the forces, leading to low morale and the belief among senior officers that their job is unimportant and unfulfilling. The inability to fill the military ranks will also eventually require painful decisions over where to deploy the limited troops and what additional alliance duties Japan can take on.

This challenge is particularly alarming given the massive disparities between the present size of the militaries of Japan and its closest allies compared with those of its primary adversaries. In 2022, the number of Japanese military personnel stood at a measly 227,843, while the United States had approximately 1.3 million active forces and South Korea about 500,000 (Seoul has around a further 3 million reserve forces). China’s military, on the other hand, features approximately 2 million active personnel, and North Korea’s about 1.2 million. Indeed, when it comes to a possible conflict between Japan and China and North Korea, retired Vice Admiral Yoji Koda told Reuters in 2022 that “manpower is the real issue.”

LESS ISN’T MORE

The effect of an aging society on defense goes beyond recruitment. It also constrains the national budget and stymies innovation. Japan’s new defense strategy, unveiled in 2022, will require an estimated $300 billion through 2027. But entitlement demands continue to dominate spending as the single largest government expenditure, with over 37.7 trillion yen ($222 billion), or 33.5 percent of the national budget, allocated for social security in 2024—three times the level in 1990. These demands will only grow as the population continues to age and the workforce continues to shrink, with increasing reliance on national health care and pension systems and a contracting tax pool to fund them. The last three decades of economic stagnation—the stock market only returned to its 1990 high in 2024—has further impeded efforts to raise revenue, and efforts by Kishida to raise taxes for defense during his term floundered.

Japan’s shrinking population is complicating the country’s efforts to develop a larger indigenous defense sector and decrease its reliance on U.S. weapons and munitions—a crucial pillar of its defense overhaul. In 2023, Japan ranked 32nd on the International Institute for Management Development’s World Digital Competitiveness Ranking—its worst placement since the list began in 2017. The country is facing engineer shortages in the vital chip industry, a shrinking college-age population, and a falling number of doctoral degree recipients, further weakening Japan’s prospects for economic productivity. This all means less brain power for research and development and less physical labor for assembly lines and transportation.

Japan’s Ministry of Defense has been forthright in acknowledging that the demographic crisis will affect national security. It outlined, in its new security strategy in 2022, how the rapid population decline would require a more efficient use of its budget and labor force. The Japanese military has tried to adapt its operations to a smaller force, including by retrofitting vehicles and ships to operate with fewer people and relying on advanced technology to carry out tasks traditionally assigned to people. In December 2024, the Ishiba government approved funding within its 2025 fiscal budget to increase wages and implement new measures to improve work-life balance in the armed forces.

Yet even with a more efficient and technologically enabled force, Japan’s military will still require manpower. Applying a strategy of so-called minimal manning—working with as few service members as possible—is not a solution but a Band-Aid. To develop, produce, and operate new and increasingly indispensable technologies, Japan will need more highly trained—and highly paid—soldiers for advanced warfare. And infrastructure such as ships require several hundred people to operate.

Fewer people will therefore mean that troops have to endure longer deployments, commanders will have less flexibility in deploying troops, casualties will exact a greater toll on the capacities of the military, and the military will face greater constraints in staffing new battalions and engaging in operations. All of this will put further stress on current service members, making military jobs even less desirable. And it will mean that Japan cannot dedicate the resources needed to become a stronger, more equal partner in its alliance with the United States, never mind take on a larger role in the Indo-Pacific.

MANAGING EXPECTATIONS

Most of the Japanese government’s proposals to address the country’s demographic challenges have thus far not gained traction. In recent years, Japanese leaders have pursued policies to encourage families to have more children. In 2023, for example, Kishida introduced a plan to double government spending on childcare support by 2030, but the new childcare law passed in 2024 under Ishiba amounts to less than half the amount Kishida outlined. Kishida’s other scheme, to pay for college tuition for families with three or more children, was widely criticized on Japanese social media as unserious and impractical, and helped sink his approval rating; although the measure passed, its effect will be almost impossible to measure for at least two decades.

Another solution that scholars and pundits often propose is to encourage more immigration; Japan has historically not welcomed many immigrants, and some analysts imagine that a significant reset of this policy will bring needed dynamism and vitality to the economy and Japanese society. But immigration is not a permanent fix. Newcomers could eventually replicate Japanese birthrates. They would also bring in new costs, namely when it comes to social integration, and the government would also eventually have to pay for further entitlements if immigrants settle and age in Japan. And in terms of recruitment to the country’s military, only Japanese citizens can join Japan’s armed forces.

In my discussions with politicians, bureaucrats, and demographers in Japan last summer, many feared that the solution to the demographic crisis is far too crass to say out loud. Japan needs more consumers, soldiers, and taxpayers, and so families need to have more children. But few ministries have implemented policies that will address the stubborn gender norms that make it extremely difficult for women to have children, maintain their careers, and enjoy a healthy work-life balance. Invoking national security needs will do little to spur couples into action. “If you want babies, you can do it and the government will support it,” one Japanese official told me. “But to argue that we have to increase the birthrate because of our national security, it is a very difficult thing to put in the right context.”

The United States can pester Japan all it wants about dedicating more resources to defense, but Japan is not likely to fulfill either country’s dream of a stronger, more equal U.S.-Japanese alliance. If it were up to Ishiba, Japan would already be on its way to reaching that goal. But there are few guarantees that Ishiba will be able to follow through on the agenda set by his predecessor, especially after his party lost its legislative majority in October. Doubling Japan’s defense spending now will strengthen the country’s national security, but such increases are unlikely to stretch into the long term, Japanese troops are not likely to be able to deploy in large numbers abroad, and the Japanese government will not eagerly turn to military force over diplomacy. Both Tokyo and Washington must adjust their expectations for what Japan—and other partners facing similar demographic declines—can reasonably achieve, especially in the long term, when the consequences of an aging and shrinking population will be even more severe.

TOM LE is Associate Professor of Politics at Pomona College. He is the author of Japan’s Aging Peace: Pacifism and Militarism in the Twenty-First Century.

Excerpts: Foreign Affairs