Wars are becoming less frequent: a response to Harrison and Wolf


  • We thank Erik Gartzke, Ismene Gizelis, Nils Petter Gleditsch, Tim Hatton, Andrew Mack, Steven Pinker, and workshop participants at the University of Essex for helpful discussions and comments. The authors are listed in alphabetical order; equal authorship is implied. Gleditsch would like to acknowledge the support of the Research Council of Norway (180441/V10).


Harrison and Wolf claim that interstate ‘wars are becoming more frequent’. This is an alarming claim deserving serious attention. It is also a highly surprising claim, since recent conflict research tends to find the opposite: incidences of violent conflict are becoming less frequent. We argue that Harrison and Wolf's claim is incorrect. We show empirically that interstate wars are in fact becoming less frequent. Other data on tensions between states below war, such as the Interstate Crises Behavior data, also suggest a decline in conflict between states. We detail how Harrison and Wolf's analysis is misleading, highlighting how their findings primarily arise as a likely artefact of their uncritical use of the Militarized Interstate Disputes (MIDs) data, and explaining why MIDs cannot be interpreted as ‘wars’. Given that Harrison and Wolf's basic premise is wrong, and wars are not becoming more frequent, we should be sceptical of their conclusions. We briefly revisit their suggested explanations for why wars may become more frequent in light of what we know about long-term trends in warfare and research on interstate war.