As World War I came to a close, German physicists were surprised to find that their position in the international scientific community had shifted drastically. Once the undisputed masters of the physical domain, German scientists were shunned by their European colleagues and shut out of meetings and institutions. Planck, who had over the last decade become an unofficial spokesman for German physics, did what he could to draw himself and his peers back into the European fold. He was motivated by more than the urge to restore the reputation of his colleagues; Planck believed that once the world accepted and respected German science, it would once again accept and respect Germany itself.
In 1919, the European countries who had fought against Germany in the war established the International Research Council, an organization which excluded scientists from its administration, meetings, and projects. The reason most often offered for this exclusion was the Appeal of the Ninety-Three Intellectuals. Scientists all over the world had been appalled by the appeal and by the support it had received throughout the German academic community. These war-mongering and ultra-nationalistic German intellectuals, they argued, were not worthy of taking part in an international community.
For Planck, the International Research Council epitomized the challenge that was facing the German scientists, and Planck began a long struggle to convince the Council that Germans should be allowed to take an equal part. The question remained as to how Planck could achieve such persuasion. Although Planck had himself publicly renounced his support of the Appeal several years earlier, he counseled his colleagues not to bother, believing that it would not help matters. Despite his own nationalistic preaching in the past, Planck now argued that science should be an international pursuit, one that rose above politics and nationalities. This led him to being a bit stubborn and hostile when he felt that non-German countries were mixing science and politics by punishing German scientists for their German citizenship.
Because he would settle for nothing less than full equality, Planck resisted the compromise offered in 1926, when the Council finally removed its ban on German scientists. Planck and his colleagues wanted more, namely an explicit renunciation of the Council's anti-German attitude. This move was directed not only at the administrators of the Council but also at their own government. The scientists, disgusted by the way the Weimar Republic had let its enemies walk all over it with the Treaty of Versailles, pointedly refused to accept what they saw as a humiliating act of charity by their former enemies. They wanted to be acknowledged rightfully as full members of the scientific community, and they didn't want to be admitted begrudgingly because of politics or pity.
Gradually, the enmity between Germany and its former enemies cooled, at least in the scientific realm. In 1927, Planck was invited to attend the Solvay Conference of 1927, even though his scientific work no longer put him at the forefront of the field. The invitation was symbolic of the new effort to reach out to the Germans in a spirit of tolerance and healing.
Despite this success, Planck could not rest; he was fighting a two front war. His attention had to be split between the struggle to get German science noticed again by the outside world and an even more important battle within his own country. He was fighting to keep German science alive.