Does the threat of third-party punishment reduce intentional civilian casualties in war? This study argues that combatants anticipate sanctions when their alliances and trade networks are dominated by nations enforcing international treaties prohibiting civilian targeting. Data from all interstate wars (1900–2003) show fewer civilian deaths occur as ratifier strength increases within these networks.

Key Insight: Sanctions deter violence against non-combatants.

* Context: Alliances & trade partnerships shape expectations of third-party enforcement during conflict.

* Mechanism: Stronger ties with treaty-signatory nations increase anticipated punishment.

* Data: Comprehensive analysis of 104 interstate conflicts from 1900–2003

Findings: Higher expected sanctions correlate strongly with reduced civilian targeting by combatants.

This reveals crucial insights about how international norms and institutional pressures influence state behavior during war. By quantifying the impact of third-party actors, this research demonstrates that strategic calculations regarding global enforcement mechanisms can significantly improve civilian protection outcomes.