To Rescue or Refrain: Unraveling U.S. Public Opinion on Military Interventions

• In Event: Popular Support and War

Abstract

Public support for US military interventions to defend victims of aggression is a complex and multifaceted phenomenon that has been extensively studied in the academic literature. However, previous research has often examined the relevant factors in isolation, leaving their relative importance and interactions unclear. To address this gap and investigate the factors shaping American citizens’ support for military interventions, we conducted a paired choice-based conjoint survey experiment with a large national sample of 3,054 US adult respondents, closely mirroring the population across key demographic features.

For the structure of the conjoint experiment, we consider eight factors that span over three different dimensions: factors related to the US, the recipient country, and the international endorsement. Participants completed eight rounds of paired scenario comparison and scenario ratings, providing a comprehensive view of the factors that influence their decision-making process.

At the US level, we probed into the impact of elite cues, gauging the influence of political party support on public opinion. We also assessed the weight of anticipated American troop casualties and economic costs, alongside the expected likelihood of military success, in shaping public sentiment. Turning to the recipient country dimension, our study examined the role of the recipient country’s regime type, its military alliance with the US, and the presence of strategically important resources. Regarding the international endorsement dimension, the endorsement from the United Nations Security Council was scrutinized as a potential legitimizing factor that could sway public opinion, reflecting the broader international consensus on the proposed military intervention.

Our findings reveal several critical insights. First, the expectation of US troop casualties is a significant factor affecting public support for military interventions, capable of swaying support by up to 17 percentage points. Similarly, the perceived likelihood of operational success is also highly influential, altering public opinion by up to 16.8 percentage points. These findings underscore the sensitivity of US public opinion to potential costs and risks of military action. Second, we find that elite cues from major political parties in the US also substantially influence support, by up to 8 percentage points. This highlights the power of partisan messaging in shaping public views on foreign policy.

Third, our results demonstrate that factors related directly to the US, including casualties, likelihood of success, and elite cues, impact American public opinion more than characteristics of the country under invasion or international endorsements. Overall, our study provides novel evidence that citizens decide whether to support military intervention based on multiple interacting factors - illuminating the complexity inherent in public attitudes toward the use of force.

We demonstrate the utility of conjoint experimental designs in modeling multi-dimensional foreign policy choices. Our findings on the primacy of US-centric factors in driving public support also challenge conventional wisdom; characteristics of the country at risk do not sway opinion as much as domestic considerations. For policymakers, our results highlight the need to convince citizens of likely success and reasonable costs when contemplating military action. Scholars and leaders alike must recognize the intricate calculus underlying public support for wars to understand the possibilities and limits of US intervention going forward.

Authors

• Ronan Tse-min Fu, Academia Sinica

• Elaine I-lien Lee, Academia Sinica