Alliances and Hierarchical Defense Commitments - Micro-Evidence from France, Germany, and Poland

Collective defense is a classic public good, yet alliance burden-sharing has almost exclusively been studied at the state level. We investigate its micro-level foundations using original survey data from France, Germany, and Poland, in which respondents report their willingness to defend four targets: their own country, the other two countries, and NATO's eastern flank. Using stacked logit models, we exploit this within-person design to identify defense hierarchies, derive solidarity gaps across defense targets, and examine both the determinants of willingness to defend and the factors that widen or narrow these gaps. We find a pronounced defense hierarchy in all three countries, with homeland defense exceeding alliance defense by 13-41 percentage points, consistent with citizen-level free-riding. Willingness to defend is systematically higher among respondents who perceive a stronger Russian threat (+8.0 percentage points), are aware of the Weimar Triangle (+10.2), have completed mandatory military service (+9.0), or have personal military contacts (+7.3). Yet the resulting solidarity gaps are far from fixed. Where citizens trust the governments of the other countries and perceive them as contributing their fair share to collective defense, these gaps narrow by up to four fifths.