After the Hemoclysm: The Likely Decline of Conventional War since 1950

We provide strong evidence of a post-1950 decline in conventional war. A survey of the qualitative literature identifies the Korean War and other post-1950 factors as spurring decline, while a quantitative analysis of Project Mars database of all conventional wars between 1800 and 2011 finds a dramatic decrease in the war-arrival rate after 1950. When we restrict attention to relatively large wars, e.g., those with killed in action (KIA) counts above the median count for the whole period, evidence for decline remains strong and is strengthened further when we use KIA per 100,000 of world population as the war-size metric. We attach Bayesian posterior probabilities to the event of a post-1950 decline for a wide range of war-size measures and ranges and prior beliefs and provide an online interactive application that allows readers to conduct their own explorations. These calculations robustly find a likely decline in conventional war.