In July 1914, the long-standing peace of Europe was shattered when the Sarajevo assassinations quickly escalated to World War I. In contrast, at the height of the Cold War in 1962, the Cuban Missile Crisis could easily have plunged the world into a thermonuclear world war, but it was ultimately resolved peacefully. Why the difference in outcome?

The historical, economic, and structural causes of war are constructed by human beings, and thus involve memories, emotions, and motives of both leaders and followers. In this presentation, I identify three psychological factors that contribute to conflict escalation: desire for power, exaggerated perception of an opponent's threat, and justification for using military force. Several lines of research, from archival studies of documents to laboratory research to surveys establish how these factors lead to war, and suggest policies to preserve peace.