Summary

What do we know about the causes and outcomes of international military conflict? Decades of research from different theoretical traditions have explored the outbreak and conclusion of international conflict from a variety of angles. Broadly speaking, scholarship about international conflict has tended to orbit around three core concepts: power, institutions, and the source of the interstate dispute. The question that remains is how well verified are the most important theories? Three influential theories seek to predict patterns of international conflict: power transition theory, which argues that shifts in power increase the likelihood of war; selectorate theory, which predicts that states that have large winning coalitions are more selective about war; and theories about issue indivisibility and war, which predict that issues that states view as impossible to divide—such as a national homeland—are more likely to lead to conflict. Each of these theories produces specific predictions, allowing an assessment of how well the evidence supports the theories’ main conjectures.

Central to understanding the causes of conflict is whether empirical work has tested these three theories using well-validated measures; whether a variety of scholars have tested the core propositions of the theory; and whether scholars have found evidence of the causal mechanisms proposed by each theory. Although each theory has garnered some support, they all fall short on one or more of these criteria. In particular, more work is needed in both measurement and evidence of causal mechanisms before scholars can be confident of the theories’ explanatory power.