Mearsheimer on Japan's Security Dilemma and Nuclear Conundrum

For students and scholars of international relations, the name John Mearsheimer needs no introduction. His theory of offensive realism, rooted in the idea that a world without a higher authority compels great powers to seek maximum power for survival, is taught in classrooms around the world.

Mearsheimer's public talks circulate widely online, some drawing tens of millions of views. Yet, in the United States, his name is rarely heard in mainstream media or Washington's policy circles. The reason is not obscurity but one of discomfort. 

Though analytically rigorous, his views often run counter to the prevailing foreign policy thinking. By stripping geopolitics down to its most elemental dynamics and rejecting the premises of liberal internationalism or neoconservatism, he advances a brand of realism that remains unfashionable in America's mainstream discourse.

That trademark approach was on full display in Tokyo on December 13, when the University of Chicago's distinguished professor returned to Japan for the first time in eleven years. Addressing a packed audience at an event hosted by The Core Forum, Mearsheimer delivered a blunt assessment of the world Japan now confronts.

China as a Peer Competitor

"We live in a multipolar world," he began, contending that the United States no longer enjoys the unequivocal primacy it held after the Cold War. "China is effectively a peer competitor, and the US–China rivalry is going to dominate international politics for the rest of this century."

Washington's own strategic planning mirrors this assessment. Since 2018, the Pentagon has formally shifted its focus from counterterrorism to great-power competition, designating China as the nation's primary "pacing challenge" in 2022.

China's rapid military buildup, expanding naval presence — now the world's largest by hull count — and increasingly assertive regional posture have reshaped security calculations across the Indo-Pacific.

But where Mearsheimer diverges from conventional wisdom is in his interpretation of Beijing's behavior. Much of today's public debate rests on the assumption that China's actions are uniquely malign. Mearsheimer rejects that framing.

"There is a powerful tendency in countries like Japan and the United States to describe the Chinese as the bad guys," he says. "But this is a fundamentally flawed way of thinking about international politics. China is simply trying to maximize its prospects for survival."

Preventing Chinese Hegemony

From Mearsheimer's vantage, great powers operate in a system without overarching authority, where survival depends on maximizing relative strength. Viewed this way, he sees Beijing's pursuit of regional dominance and its efforts to curb American influence as a natural extension of that imperative.

To sharpen his point, he turned to a comparison that touches on a sensitive period in Japan's history. Had Japan today been overwhelmingly stronger than its neighbors, he says, it would pursue regional hegemony for the same reason China does — just as it did between 1868 and 1945.

The conclusion was unmistakable. Japan, the US, and their like-minded allies would, by any means necessary, act to prevent China from achieving regional hegemony. That goal, in turn, inevitably places them in direct opposition to the region's nuclear power.

Translating that strategic imperative into practice is far more complicated. Thwarting Chinese dominance is easier said than done, not least because the rivalry is concentrated around several flashpoints that carry a constant risk of escalation. Mearsheimer identifies three in particular: the Senkaku Islands, the South China Sea, and Taiwan.

Of these, Taiwan looms largest, he says. Control of the island, Mearsheimer argues, would dramatically enhance China's ability to project military power beyond the first island chain, tilting the regional balance decisively in Beijing's favor.

Making War Less Likely

Still, Mearsheimer stresses that a successful invasion or blockade is far from guaranteed. In conventional military terms, the balance, for now, still favors the defending coalition. If Japan, the US, and Taiwan were to mount a full-scale coordinated defense, he says, China would be unable to conquer the island — at least for the foreseeable future.

This reality helps explain why Taiwan now sits at the center of Washington's strategic planning in the Indo-Pacific, not only because of its democracy or technological importance, but because of its pivotal geopolitical position in the region.

For decades, Washington has relied on a policy of "strategic ambiguity" toward the self-governing island, deliberately declining to state whether it would intervene militarily in the event of a Chinese attack. In practice, that ambiguity has steadily narrowed.

During his presidency, Joe Biden publicly stated on several occasions that the US would come to Taiwan's aid if it were attacked, reinforcing a firmer articulation of American commitments. Although White House officials later moved to qualify those remarks, Mearsheimer notes that "the signal to Beijing was unmistakable."

While rhetoric surrounding Taiwan has grown less predictable under President Donald Trump, the underlying policy holds steady. The administration continues to approve major arms sales to Taipei, and the latest National Security Strategy states that "deterring a conflict over Taiwan, ideally by preserving military overmatch, is a priority."

Mearsheimer sees such signaling as central to deterrence. Extending the same logic to Japan, he praised Prime Minister Sanae Takaichi's November 7 parliamentary remarks that a Taiwan contingency could threaten Japan's survival, describing them as "a smart thing to say."

By clarifying the consequences of aggression, "they make war less likely," he says. "If China starts a war, it will face an almost certain defeat."

The Nuclear Conundrum 

Perhaps the evening's most provocative moment came when Mearsheimer turned to the subject of nuclear weapons, a long-standing taboo yet one increasingly difficult to ignore.

"In an ideal world," he says flatly, "Japan would have nuclear weapons now, because nuclear weapons are the ultimate deterrent."

Such a comment would once have been inconceivable in Japan's postwar discourse. Yet it drew sustained applause from the audience. For a nation that knows all too well the horror of atomic devastation, the response appeared less a full-on endorsement than an acknowledgment of the growing unease surrounding the archipelago's security environment.

Some estimates suggest China now possesses more than 600 nuclear warheads, a number the US Defense Department believes could exceed 1,000 by 2030. North Korea, meanwhile, continues to advance its nuclear and missile arsenal, conducting repeated tests in defiance of international sanctions. 

Japan, by contrast, remains formally bound by its three non-nuclear principles of not possessing, not producing, and not introducing nuclear weapons onto its territory.

But despite the deteriorating security landscape in Northeast Asia, Mearsheimer was quick to explain why he thinks Washington has, and will continue to, oppose a nuclear-armed Japan.

"The United States wants to make sure that if a crisis ever breaks out involving an ally, Japan does not have a finger on a nuclear trigger," he says, out of concern that it could drag Washington into an unwanted nuclear confrontation.

Rethinking the Taboo

But deterrence, he adds, rests as much on belief as on hardware — and belief cuts both ways. Under the current framework, Japan can never be entirely certain that the United States would risk its own cities for Tokyo in the event of a nuclear clash.

If Washington were to hesitate at a decisive moment, Mearsheimer says, it would give Japan "a very powerful incentive" to acquire its own nuclear deterrent.

That logic, once confined to small circles, is reaching a wider public debate. A Reuters investigation published in August, for example, found increasing political and public openness to revisiting Japan's non-nuclear principles, particularly the ban on allowing nuclear weapons onto Japanese soil. Some policymakers worry that this third tenet could undermine overall American deterrence.

For now, the Japanese government maintains that the three principles remain intact. But the applause that greeted Mearsheimer's lecture suggests that the boundaries of debate, though incremental, are indeed shifting.

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Author: Kenji Yoshida