From 1929 to 1945, Harnack House was the clubhouse of the Kaiser Wilhelm Society (KWG), the precursor to the Max Planck Society. It was a service center for the surrounding campus and a guest house for scientists visiting from abroad. Following the First World War, Germany lost its position as a scientific and academic leader and was excluded from the scientific community. As a result, Harnack House played a role in foreign policy during the Weimar Republic. Even after the Nazis seized power in 1933, Harnack House retained a clear international focus. The connections to the international scientific community remained up until the Second World War broke out; indeed, the National Socialist regime also used Harnack House as a foreign-policy tool – a platform for its relations with friendly nations.