He opposed the Italian invasion of Libya in 1912, but at the outbreak of the First World War, despite his anti-militarist ideas, he became an ardent supporter of the interventionist camp on the side of the Triple Entente. He launched a vigorous campaign against Avanti, the organ of the Italian Socialist Party (PSI), when Benito Mussolini was removed as chief editor, and openly criticized the PSI for what he considered Bolshevik sympathies.