Before the words “nuclear nonproliferation” entered official discourse, the term “non-diffusion” (or “non-dissemination”) of nuclear weapons was used routinely. In part stemming from the negotiations over Berlin, during 1962-1963 the Kennedy administration held talks with allies and adversaries on the possibility of a non-diffusion agreement which included Germany. In light of a recent Soviet proposal, INR veteran Soviet expert Sonnenfeldt explained why Moscow had moved away from earlier proposals singling out West Germany and was focusing on the general applicability of a non-diffusion agreement.

This lengthy report was State Department Bureau of Intelligence and Research's contribution to the first National Intelligence Estimate on the nuclear proliferation, NIE 100-6-57. Written at a time when the United States, the Soviet Union, and the United Kingdom were the only nuclear weapons states, the “Fourth Country” problem referred to the probability that some unspecified country, whether France or China, was likely to be the next nuclear weapons state. Enclosed with letter from Helmut Sonnenfeldt, Division of Research for USSR and Western Europe, to Roger Mateson, 4 June 1957, Secret