Forty years ago, the Stockholm Document turned the political promise of the 1975 Helsinki Final Act into a more practical system of confidence-building. Amid the Cold War, Europe’s East and West did not disarm, abandon deterrence or begin to trust one another. Instead, they agreed that military competition could be made safer through prior notification, observation, information exchange and verification. The lesson was modest but durable: adversaries do not need trust to reduce uncertainty. That...