Public Perceptions About What the US Would Do if North Korea Invaded South Korea
Do Americans and South Koreans expect the United States to defend South Korea against a North Korean invasion? My original survey data finds nearly a quarter of Americans believe the US would do nothing, while South Koreans are more confident that the US will at least supply weapons and intelligence to the South. More surprising, more than one in twenty Americans and one in ten Koreans surveyed supported the US using nuclear weapons in this scenario. The results highlight challenges in addressing expectations and raise concerns about public understanding of the consequences of a US response.
President Trump is expected to demand higher military cost shares from South Korea and Japan, raising questions about whether either ally is willing to pay more and if not, how might US defense commitments change. In South Korea, this was a major point of contention during Trump’s first term. The South Korean public largely opposed Trump’s previous $5 billion increase demand, even while supporting the alliance more broadly. But given the continued antagonism over burden sharing, Trump’s previous threats to withdraw US troops from the Korean Peninsula, and even his treatment of other allies, it remains unclear whether the US and South Korean public truly believe the US will still defend South Korea in case of a North Korean attack.
The Costs of Conflict
Estimating even short-term casualties of such an invasion is challenging given the capabilities of both sides, the expected support of the US and perhaps others, and the physical proximity of the demilitarized zone to Seoul. North Korea’s assortment of missiles, rocket launchers, and long-range artillery, more broadly, may still inflict mass casualties to the densely-populated Seoul even if South Korea was able to thwart efforts through counter-artillery and missile defense systems. A US-backed South Korea would maintain several advantages in the long run in such a conflict, especially air superiority, but this would not negate the initial challenges and the potential for urban warfare and mass panic. One estimate assumed costs of up to $20 billion dollars for the US and $2.5 billion for China. A 2017 Pentagon simulation expected 20,000 deaths daily in South Korea, while the US Department of Defense estimated 200,000-300,000 South Korean and US military casualties in the first 90 days. A war could also incur $40 trillion in property damage, with a potential decline of 3.9% of global GDP in the first year.
Such scenarios also typically assume that an initial invasion does not include North Korea’s use of weapons of mass destruction, despite the belief that the country possesses both biological and chemical weapons alongside a small stockpile of nuclear warheads and Kim Jong Un’s own statements about expanding the country’s number of warheads and that the weapons are not purely defensive. South Korea’s increased interest in their own nuclear capabilities or the redeployment of American nuclear weapons further complicates estimates. The endurance of an informal nuclear taboo now becomes more difficult to continue in an era of greater international uncertainty.
Public Perceptions
Previous research gives some indication of public expectations. A 2024 Chicago Council survey finds a majority of Americans across parties support maintaining US military bases in South Korea, with other surveys finding tepid support for closing bases and generally a supportive public for bases. However, the US public increasingly appears disinterested in an active foreign policy, preferring an inward-looking policy consistent with President Trump’s “America First” campaign rhetoric. Meanwhile, South Koreans appear generally supportive of the US military presence, and views of Trump’s cost demands did not seem to influence this support. A history of support for South Korea’s defense however does not ensure future support, and as the deterioration of US relations with Canada attests, changes may be abrupt.
To address perceptions of what the US would do for South Korea’s defense, I conducted two national web surveys, using quota sampling for age, gender, and region. The first, conducted from February 12-26 via the company Centiment, surveyed 522 Americans. The second, conducted from February 24-27 by Macromill Embrain, surveyed 1,000 South Koreans. The surveys did not explicitly remind respondents that the US maintains a military presence of over 28,500 personnel in South Korea. While this may be seen as common knowledge to Korea-watchers, it may not be, particularly to a segment of the US population disinterested in international affairs, and thus exclusion of this information upfront may better provide a baseline view of beliefs of what the US ideally should do.
Starting with the US, nearly a quarter of respondents (24.33%) expected the US to do nothing, while the most common response was to supply aid and intelligence (49.43%), with 37.36% thinking the US should commit troops and air support. This suggests perhaps ignorance of the current presence of US personnel in-country, a belief that additional commitments would not be warranted, or sensitivity to potential casualties. Perhaps most alarming was that 12.84% of respondents supported the use of tactical nuclear weapons. At first glance, this suggests a stark willingness to break the nuclear taboo that has held since the end of World War II, but another interpretation may be that this existential threat to South Korea would require such a significant response. Moreover, we see limited differences between Democrats and Republicans, suggesting that, despite an increasingly polarized view of foreign policy, and a majority of respondents (60.54%) stating the “we should pay less attention to problems overseas and concentrate on problems at home,” this does not translate to how to respond to North Korea.
Moving to the South Korean data, we see several differences. First, South Koreans overall were far less likely to believe the US would do nothing (7.10%), perhaps due to being cognizant of the US military presence already in the country. This may also explain the firm belief that the US would supply aid and intelligence. Regarding expectations of the US committing troops and air support, overall rates are only slightly higher than those in the US (41.3% vs. 37.36%), perhaps suggesting a hesitation that the US would commit additional resources if traditional efforts at deterrence had failed. Of particular note, South Koreans were far more expectant that the US would use tactical nuclear weapons, 21.2% of respondents overall. We also see more of a partisan distinction here between the liberal Democratic Party (DP) and the conservative People Power Party (PPP), with the PPP less likely to believe the US would provide aid and assistance, but more likely to commit troops or use nuclear weapons.
Conclusion
Public opinion does not dictate foreign policy decisions, but it can shape leaders’ options and provide justification for actions taken. The findings here reveal a notable gap: South Koreans show greater confidence that the US will respond if North Korea invaded the South, including the possibility of using nuclear weapons, while US respondents were over three times more likely to believe the US would do nothing in this scenario.
While both publics acknowledge the gravity of the situation, the results point to concerns that overconfidence in South Korea may drive expectations, limiting consideration of a US that fails to respond sufficiently. Admittedly, capturing public opinion about a hypothetical is marred with “what ifs,” especially where the end result may lead to a conflict of the magnitude not seen in the region in decades, adding uncertainty to supply chains. Public views about conflict naturally change once conflict moves from the abstract to the concrete.
For the US, addressing the differing expectations of both populations could inform more strategic communications about its role in defending South Korea and improve overall reassurance even amid ongoing disputes within the alliance over such issues as military burden sharing. Furthermore, the apparent willingness to employ tactical nuclear weapons warrants broader consideration as to what kind of effects it would have on the Korean Peninsula and whether the public fully conceptualizes what breaking this taboo might mean for future conflict.