biostudies-literatureCranmer SJAlexander von Humboldt-StiftungHoward W. Odum Institute, University of North Carolina at Chapel HillJames S. McDonnell FoundationNational Science Foundation11812-6https://www.ebi.ac.uk/biostudies/studies/S-EPMC4586843biostudies-literatureUnknown112(38)Network science has spurred a reexamination of relational phenomena in political science, including the study of international conflict. We introduce a new direction to the study of conflict by showing that the multiplex fractionalization of the international system along three key dimensions is a powerful predictor of the propensity for violent interstate conflict. Even after controlling for well-established conflict indicators, our new measure contributes more to model fit for interstate conflict than all of the previously established measures combined. Moreover, joint democracy plays little, if any, role in predicting system stability, thus challenging perhaps the major empirical finding of the international relations literature. Lastly, the temporal variability of our measure with confProceedings of the National Academy of Sciences of the United States of AmericaKantian fractionalization predicts the conflict propensity of the international system.PMC4586843SES-1357622SES-1461493220020315Fellowship for advanced researchersSeed grantDMS-0645369Menninga EJCranmer SJMucha PJfalseKantian fractionalization predicts the conflict propensity of the international system.Network science has spurred a reexamination of relational phenomena in political science, including the study of international conflict. We introduce a new direction to the study of conflict by showing that the multiplex fractionalization of the international system along three key dimensions is a powerful predictor of the propensity for violent interstate conflict. Even after controlling for well-established conflict indicators, our new measure contributes more to model fit for interstate conflict than all of the previously established measures combined. Moreover, joint democracy plays little, if any, role in predicting system stability, thus challenging perhaps the major empirical finding of the international relations literature. Lastly, the temporal variability of our measure with conf2015-01-01T00:00:00Z2015 Sep2025-05-31T22:55:27.079Z2025-05-31T22:55:27.079ZS-EPMC45868432633897710.1073/pnas.1509423112