On 10 June 1963 President John F. Kennedy gave a speech that changed the world. His commencement speech at American University helped to spur the signing of a world-changing agreement between the Soviet Union and the United States—the Partial Nuclear Test Ban Treaty. This episode of peacemaking is remarkable for two reasons. First, it arguably helped to save the world, since the nuclear confrontation at that stage of the Cold War was not a ‘stable balance of terror’, as sometimes described, but rather a highly unstable situation that was prone to accidents, misjudgements and potential disasters. Second, this was an episode of statesmanship in which presidential leadership played a crucial role. Following the Cuban Missile Crisis, Kennedy understood that he bore sole responsibility on the US side to find a way back from the brink of nuclear war. He used the ‘peace speech’ to create a novel kind of peace diplomacy, and worked together with his counterpart, Soviet leader Nikita Khrushchev, to pull the superpowers back from this precarious brink.