World War I destroyed the system of international competition / cooperation between the major scientific nations of Europe and America and inaugurated an era of chauvinistic manifestos, isolation, and academic boycotts that lasted more than ten years. Niels Bohr’s Copenhagen Institute of Theoretical Physics provided an important but rare exception to the rule, by continuing internationalist commitments throughout the 1920s and creating one of the few places where scholars from hostile nations were encouraged to meet and collaborate. This paper examines the diplomacy, resources, and strategies that allowed Bohr to develop an international “center on the periphery” of European science, in a tiny country with limited possibilities.

1. Scandinavian internationalism. Denmark’s neutral status allowed it to seek larger influence in world science by mediating between hostile greater powers. Sweden pursued a similar strategy via the Nobel prizes, while Denmark established a state foundation after WWI to fund its scientists’ international activities. Bohr relied on it to invite the first foreign visitors to his institute, who mostly came from small countries of Northern and Central Europe.

2. American philanthropy. Bohr’s contacts with the Rockefeller Foundation established with the help of the Danish diaspora resulted in a relatively small – by Rockefeller standards – but very timely institutional grant. The Foundation’s first project to support European science after the destructive war also implied continuing investment in the form of IEB fellowships.

3. Postdoctoral revolution and hyperinflation. Unlike German research “schools,” Bohr’s institute attracted postdoctoral visitors from abroad, rather than PhD students. During the dire times of inflation, this new career model for European scientists provided a much needed temporary substitute for the financially undermined position of Privatdozent at German universities and an additional motivation for up and coming scientists to come to Copenhagen.

4. Quantum Mechanics as Knabenphysik. The difficulties Bohr’s own program of atomic physics encountered by the mid-1920s were resolved by a combination of new skills and training brought in by international visitors, such as Klein, Pauli, Heisenberg, Slater, Dirac, and later also Gamow, Landau, Rosenfeld, and others. The postdoctoral culture of doing science, nurtured by the Bohr Institute, culminated in a radical quantum mechanical revolution by 1927.