During the First World War, he relocated to Switzerland, where he argued that socialists should work toward converting that "imperialist war" into a continent-wide "civil war" in which the proletariat could overthrow the bourgeoisie.
Pada Perang Dunia Pertama, ia berpindah ke Swiss, dimana ia menyatakan bahwa sosialis harus bekerja terhadap peralihan "perang imperialis" ke "perang saudara" seluruh benua dimana proletariat akan melengserkan kaum burjois.