The Triggers of War Disentangling the Spark from the Powder Keg

The onset of interstate conflict often hinges on seemingly random events (‘sparks’) such as the assassination of Franz-Ferdinand in 1914. However, the literature on the causes of interstate war has mostly focused on identifying fertile grounds (‘powder kegs’), ignoring these intricacies of history that are typically treated as noise. Yet this approach cannot explain why certain fertile grounds remain peaceful, or why wars start precisely when and where they do. Here, we measure and demonstrate the importance of these idiosyncratic factors with monthly information about sparks from three different sources: a) one hundred years of newspaper articles; b) two hundred years of government bond yields; and c) fine-grained event-data. These measures of triggers significantly improved our ability to explain and predict conflict. In particular, we found that fertile grounds or the occurrence of a trigger are both prone to conflict, but it is their combination that is disproportionately dangerous.