Defense treaties increase domestic support for military action

Using survey experiments in a new article, Jeffrey D. Berejikian and Justwan Florian show that when Americans are informed about the U.S.-South Korea mutual defense treaty they are more willing to support the use of U.S. combat troops in South Korea and accept casualties.

American political leaders often frame U.S. security interests by emphasizing the specific details of U.S. defense commitments. For example, during a recent high-profile diplomatic visit to the Philippines in July of 2021, Secretary of State Blinken privately affirmed the US commitment to President Duterte. The United States also signaled its intentions to China directly. An American warship was deployed to conduct freedom of navigation operations in the South China Sea to coincide with the visit.

However, in addition, Secretary Blinken took time to both publicly call attention to the specific details of a longstanding alliance between the US and Philippines and explain its meaning; “We also reaffirm that an armed attack on Philippine armed forces, public vessels, or aircraft in the South China Sea would invoke US mutual defense commitments under Article IV of the 1951 US-Philippines Mutual Defense Treaty.”

When political leaders focus public attention on existing security commitments in this manner, it is unlikely that they are only attempting to send a signal to potential adversaries. The conventional wisdom is that, in direct state-to-state communication, actions speak louder than words. For instance, as noted above, during Blinken’s trip the US sent a clear signal to China’s leaders by detaching a naval vessel to the region.

We believe that public statements are better understood as political acts designed to mobilize domestic opinion and communicate to potential adversaries that there is sufficient popular support to follow through on promises to defend a security partner. Indeed, mobilizing domestic political support within an alliance during a crisis is critical to the success of deterrence threats, and emphasizing formal security commitments is, in part, intended as a guardrail against shifting domestic foreign policy preferences.

So, does this communication strategy work? The answer is unclear. Foreign policy research has traditionally focused on the degree to which formal alliances shape the expectations of external audiences—allies and adversaries—in the lead-up to conflict. Interestingly, recent scholarship has demonstrated that international law sometimes also works in the opposite direction; it can shape domestic attitudes about conflict behavior.

For example, there is evidence that the public is less likely to support military action when it violates explicit legal commitments to protect human rights. This result extends to the broader obligation that governments should attempt to protect civilians during conflict.  However, because the primary focus of existing research is on human rights law that emphasizes moral obligations to others, this scholarship might not extend to self-interested national security concerns.

To answer this question directly, we conducted a novel survey experiment on a representative sample in the United States. We presented respondents with a narrative describing a military crisis on the Korean peninsula. Half of our respondents received a cue about the American mutual defense treaty with South Korea. The other half of our respondent pool did not receive this treatment. Subjects were then asked (1) whether they would support the use of U.S. combat troops in defense of South Korea, (2) how many U.S. military casualties they would be willing to accept, and (3) how many North Korean civilian casualties they would tolerate.

In a second wave, respondents received a stronger and more detailed experimental treatment that included information about the specific content of the U.S.-South Korean defense agreement. In addition, our experiment included several questions designed to evaluate the causal mechanisms by which defense treaties might potentially influence public support for military action.

Our research produced several interesting findings. First, emphasizing the defense treaty between Washington and Seoul increased support for military action on behalf of South Korea. However, the magnitude of this effect depends on the specificity of the information provided. Merely noting the fact of a prior commitment only affects attitudes of self-declared Independents. Democrats and Republicans, by contrast, were initially less responsive to our subtle priming on the U.S-Korean defense agreement. However, once individuals receive more detailed information describing the specific legal nature of the treaty – modeled on the kind of statements by American officials noted above – the gap between Independents and partisans largely disappears.

Second, we find that the reason defense treaties increase support for military action is that they elicit a belief that the United States is morally obligated to defend its ally and that backing down damages America’s international reputation. Third, formal alliances increase public “casualty tolerance.” Individuals in our treatment groups were both more tolerant of U.S. military deaths and more willing to accept North Korean civilian casualties than other respondents in the study. Interestingly, the subtle prime only influenced casualty tolerance among strong conservatives. However, again, as subjects received information about the specific legal nature of the U.S. obligation the gap between strong conservatives and others largely disappeared.

So, is framing conflict decisions around prior security commitments an effective way to shape public perceptions about conflict? The results reported here suggest that it is. Highlighting an existing promise to defend allies increases public willingness and resolve for military action. We find that this effect is not uniform across individuals and that support for military action and casualty tolerance increases as people receive more specificity about their country’s obligation.

These results demonstrate that security commitments, in addition to shaping the expectations and incentives of external actors, also contour the domestic political incentives for foreign policy action. This is, in part, why pollical leaders take such great pains to detail the nature of their country’s defense obligations to domestic audiences, even as they are communicating directly with allies and potential adversaries. Taken as a whole, these findings reveal a nuanced set of relationships between security commitments and individual-level attitudes about conflict and, as a result, generate new insights into the conditions under which leaders can use existing security agreements to mobilize the public.

Jeffrey D. Berejikian is a Josiah Meigs Distinguished Teaching Professor at the University of Georgia, and Associate Professor in the Department of International Affairs. Florian Justwan is an Associate Professor of Political Science at the University of Idaho. They are the authors of “Defense treaties increase domestic support for military action and casualty tolerance: Evidence from survey experiments in the United States”, Contemporary Security Policy, available here.


Leave a Reply

Your email address will not be published. Required fields are marked *