While interstate relations are frequently appealed to explain why states intervene in civil wars, their influence on the dynamics and trajectories of these conflicts remains insufficiently studied. Rather than simply assuming the relations between opposing interveners, or between the conflict country and rebel-supporting states as being hostile, I argue that these relationships are more nuanced and accordingly exert varying effects on civil war trajectories. Specifically, I hypothesize that greater misalignment in the foreign policy positions of the involved states intensifies civil wars by increasing battle-related fatalities. This occurs as external sponsors are incentivized to escalate their support for their preferred side, driving more decisive military engagements. To test this hypothesis, I make use of dynamic national ideal points derived from individual states’ voting behavior in the United Nations General Assembly. These ideal points allow me to estimate a continuous measure of the distance between states’ foreign policy positions. Using a Quasi-Poisson regression model, I analyze all conflict dyads between 1989 and 2017 that experienced either opposed or rebel-sided interventions. The results partially support the hypothesis: greater misalignment in the foreign policy preferences of opposing interveners significantly increases conflict intensity, while the relationship between the conflict country and the rebel-supporting sponsor does not produce statistically significant effects. These findings underscore the importance of the international system in shaping civil war dynamics, independent of the conflict-affected state itself. They demonstrate that polarized interstate relations amplify conflict intensity, irrespective of the foreign policy alignment of the civil war country.