In 1914, when World War I broke out, Zeth Höglund together with Ture Nerman represented the Swedish-Norwegian members of the Zimmerwald Conference, the international socialist anti-war movement which gathered in the small Swiss village of Zimmerwald.
The Left of the Zimmerwald Congress was made up of eight out of 38 people: Lenin, Zinoviev (Russia), Jānis K. Bērziņš (Latvia), Karl Radek (Poland), Julian Borchardt (Germany), Fritz Platten (Switzerland), Zeth Höglund and Ture Nerman (Sweden).