On the frequency and severity of interstate wars

TL;DR

This paper revisits Richardson's hypothesis on conflict patterns, confirming that the frequency of wars follows a Poisson process and their severity follows a power-law distribution, using modern data and statistical methods.

Contribution

It provides updated empirical evidence supporting Richardson's original claims with rigorous analysis and discusses implications for understanding conflict mechanisms.

Findings

War frequency follows a Poisson process.

War severity follows a power-law distribution.

Supports Richardson's original hypotheses with modern data.

Abstract

Lewis Fry Richardson argued that the frequency and severity of deadly conflicts of all kinds, from homicides to interstate wars and everything in between, followed universal statistical patterns: their frequency followed a simple Poisson arrival process and their severity followed a simple power-law distribution. Although his methods and data in the mid-20th century were neither rigorous nor comprehensive, his insights about violent conflicts have endured. In this chapter, using modern statistical methods and data, we show that Richardson's original claims appear largely correct, with a few caveats. These facts place important constraints on our understanding of the underlying mechanisms that produce individual wars and periods of peace, and shed light on the persistent debate about trends in conflict.