In a newly published article “Allied Commitments and Public Support for Military Interventions: A Cross-National Experiment,” Michal Smetana, Marek Vranka, and Ondrej Rosendorf analyze whether formal alliance treaties boost public willingness to support military interventions and whether this effect holds beyond the Western world.
The study employed a text-based vignette experiment in which participants were randomly assigned a fictional scenario describing an armed aggression against an unnamed country. Using a 2×2×2×2 full-factorial design, the researchers manipulated four attributes:
whether the victim had a military alliance with the participant's country,
whether the victim was a democracy,
whether the participant's country had high security and economic stakes in the conflict,
and whether the intervention would be costly.
After reading the scenario, participants indicated their support for sending their country's military to stop the invasion on a five-point Likert scale.
Using this pre-registered survey experiment across nationally representative samples in six countries (the United States, the United Kingdom, Russia, China, India, and Brazil), their study provides first experimental evidence that formal alliance commitments shape public support for military interventions globally. The effect is comparatively weaker in non-Western, non-NATO countries. In other words, citizens in NATO member states are more strongly influenced by alliance obligations when forming attitudes on military interventions than citizens in non-Western countries.
Moreover, their data shows a more nuanced pattern of heterogeneity in public support for military interventions than the simple NATO/non-NATO or Western/non-Western divide. The findings reveal a clear order in support for military interventions: the largest alliance effect appears in the United Kingdom, followed by the United States, Russia, and China, with the smallest effects in India and Brazil. These cross-national differences may reflect, among other factors, the recent shifts in the U.S. approach to NATO and the greater salience of Russia and China in contemporary geopolitics relative to India and Brazil.
Their data also highlights meaningful differences in baseline support for military action across countries, with Russian citizens particularly averse to defending the attacked country under any condition, while Chinese and Indian citizens were relatively supportive of military action even when the victim was not a formal ally.