Many of America’s allies have little faith that huddling under America’s nuclear umbrella will keep them safe. “The conventional wisdom has been that the threat of nuclear retaliation by the U.S. is enough to defend our junior non-nuclear allies,” says Jung Jae Kwon, a political science doctoral student at MIT. “But this threat is not as credible as is often believed, and the allies do not simply want to depend on it for their security.”

Kwon has been researching defense strategies of American client states, gathering data to analyze the security policy and military postures of frontline states that came to rely on U.S. nuclear protection during and after the Cold War.

Scholars in the security field argue that reliance on nuclear deterrence makes sense in a world full of uncertainties, and that formal treaties invoking this deterrent offer ample reassurance to junior allies. But Kwon’s historical studies show that “many allies want enough capability of their own to prevail when a conflict begins.”

His dissertation illuminates an area of security studies that has not been deeply investigated: what America’s allies believe they need to guarantee their survival.

“The literature on extended nuclear deterrence tends to focus on only the American perspective,” he says. “No one has advanced the argument that America’s allies want to be sure they have a plan and can respond to an immediate threat.”

In an era increasingly rocked by superpower jockeying, climate, energy, and pandemic crises, Kwon believes that his research “has immediate implications for today’s most pressing security questions.”

Nuclear: not a one-stop solution

Kwon arrived at MIT in 2017 broadly interested in the drivers of war and conditions that bring peace. With the guidance of security studies faculty Barry Posen, Ford International Professor of Political Science; Vipin Narang, the Frank Stanton Professor of Nuclear Security and Political Science (now serving in the Biden Administration as principal deputy assistant secretary of defense for space policy); and Taylor Fravel, the Arthur and Ruth Sloan Professor of Political Science, Kwon sharpened his focus.

“I wanted to understand how non-nuclear states achieve security,” he says. “As a devastating threat to human civilization, nuclear weapons represent an ongoing challenge that must be faced, especially as nations like Iran and North Korea continue to develop their own nuclear programs.”

To understand the security perspectives of America’s non-nuclear allies and how their military postures shift in response to heightened levels of risk, Kwon decided to investigate South Korea, Taiwan, West Germany, and Norway — nations that began sheltering under the U.S. nuclear umbrella during the Cold War. Digging into these countries’ diplomatic records, and other archival sources, he has learned that these states did not embrace nuclear deterrence as a one-stop solution to their security needs.

“When conflicts arise, these allies don’t want to give up territory or lose anything,” says Kwon. “They ask for plans where they have a viable option for victory.”

One example Kwon cites is South Korea, where the U.S. stationed tactical nuclear weapons. “But the U.S. didn’t give South Korea any control over the deterrent, no mechanisms for coordination when it came to nuclear planning,” he says. As a result, South Korea tries to maintain superiority in conventional power against North Korea. “It’s their fate; they don’t just want to rely on the U.S. for security,” he says.

And West Germany, America’s most important ally in Western Europe during the Cold War, “wanted assurance from the U.S. that nuclear weapons would be used first,” says Kwon. “They were overwhelmed by conventional Soviet military power, and wanted to assert more control over the U.S. nuclear threat.”

With the end of the Cold War and dissolution of the Soviet Union, European allies grew less concerned about attacks from their neighbors, and more content to rely on the U.S. nuclear deterrent. But recently, the war in Ukraine has shifted defense postures, says Kwon, prompting allies’ calls for greater conventional military presence along Europe’s eastern border. In East Asia, North Korean nuclear buildup has led to South Korean demands for a greater U.S. commitment and a more visible nuclear presence. “If South Koreans feel they are not provided with sufficient capability, you’ll see more tensions surface in the relationship.”

Military service and a personal reckoning

Although Kwon grew up in Seoul, South Korea, he did not become interested in international relations and security matters until much later. His family business was front and center, and like other South Korean households, they were desensitized to the “constant danger represented by North Korea,” says Kwon. He attended a boarding school in the United States, then Harvard University, where he concentrated in government and contemplated a career in law.

All that changed with Kwon’s mandatory military service, which began after his sophomore year. Initially placed with an infantry division as a mechanic, Kwon sought out and won an opportunity to serve as a translator on a South Korean unit of a U.N. peacekeeping mission in South Sudan in December 2013. Then civil war broke out.

“It suddenly became a huge humanitarian mission, with tens of thousands of refugees flooding in to escape the shooting, and all hell broke loose, literally,” he says. “We were caught in the middle of it, with shells falling into our compound, and I was caring for patients, and then we were helping to bury the dead.”

Shaken by this experience, with a newly awakened interest in matters of war, peace, and international relations, Kwon returned to Harvard for his junior year. He turned his attention to China and its expanding impact on the world. Immediately after graduation, Kwon left for a master’s program at Peking University, where he wrote a thesis on Chinese peacekeepers in United Nations missions. He arrived at MIT straight from China, to pursue East Asian politics and security issues, and his dissertation topic on the security of non-nuclear allies of the United States.

While the Covid pandemic slowed his research, Kwon has been methodically excavating historical records for useful data. “Reading diplomatic records is my biggest pleasure, because history comes to life,” he says. “Examining correspondence between Eisenhower and Chiang Kai-Shek makes the topics I’m studying more real.”

Extracting historical data for his case studies has been slow, painstaking work, but based on the research he’s completed to date, Kwon believes that both scholars and security experts will find his insights useful.

“My biggest takeaway is that allies won’t be assured simply by gestures of solidarity, formal alliance treaties, or even the huge nuclear arsenal the U.S. possesses,” he says. “Allies face specific security challenges and will seek the capability to enable them to prevail when conflicts arise, raising the likelihood of arms races.” If the U.S. fails to provide the capability they seek, “which won’t happen on the cheap,” he says, “we might see attempts by these allies to build their own nuclear weapons.”