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Scheidemann's political activities peaked during the First World War and the Weimar Republic. During the First World War, he was a member of the Reichstag and a leading member of the Social Democratic Party of Germany (SPD). In the Weimar Republic, he served as Chancellor of Germany from 1919 to 1920. He was a key figure in the German Revolution of 1918 and the establishment of the Weimar Republic.