I first came across the subject of this study through Roger Donaldson's documentary motion picture Thirteen Days about the Cuban missile crisis of 1962. Reading later about the crisis, I was intrigued by the fact that President Kennedy had read Barbara Tuchman's Pulitzer Prize winning Guns of August, a book that described the paradoxical circumstances through which, in 1914, Europe stumbled into a ‘war which nobody wanted’. There are good reasons to believe that Kennedy took the lessons of the book seriously. He understood that the confrontation with the Soviet Union over the deployment of nuclear missiles on Cuba could lead to nuclear war even though both he and Khrushchev knew that such a war would be suicidal, and that neither of them could fully control what Thomas Schelling described as the ‘dynamics of mutual alarm’. This understanding weighed heavily on Kennedy and probably on Khrushchev, too.

Not only was it inspiring to learn that an academically oriented book like the Guns of August could make a difference in world policy, it also struck me that a central element in the course of the Cuban missile crisis, the threat of force, was paid virtually no attention in the international law literature. Article 2(4) of the UN Charter expressly forbids states to take recourse to the threat of force. Yet what is to be understood by that prohibition, and how it has performed against the backdrop of sixty years of state and UN practice, has been left entirely unexplored.