Frequency and intensity of Western Wars (1600–1945). The 1618-1648 interval marks the Thirty Years' War, the 1789-1815 interval marks the Wars of the French revolution and the Napoleonic Wars, and the 1914-1945 interval marks World Wars I and II. (From Krus, D.J., Nelsen, E.A. & Webb, J.M. (1998) "Recurrence of war in classical East and West civilizations". Psychological Reports, 83, 139-143).