Mussolini began his political career as a revolutionary Socialist Party (PSI) member and leader who went to prison for his anti-war activities during the 1911-12 Tripolitan War with Turkey and participated in the expulsion of reformists from the PSI in 1912. When war erupted in 1914, Mussolini - now a PSI city councilman in Milan and editor of the party's nation-wide paper, Avanti! - initially opposed Italy's entry in the conflict. However, by October 1914 Mussolini called for a reassessment of the situation and argued that Socialists, and Italy, could not simply remain passively neutral.
Shortly thereafter, with the surreptitious aid of money from Italian industrialists and then the French, Musssolini broke with the PSI and founded his own paper, Il popolo d'Italia, which called for Italy's intervention on the side of the Entente. He was expelled from the party and thereby joined others of the Left, such as the revolutionary syndicalists Alceste De Ambris and Arturo Labriola, in calling for revolutionary war.
Mussolini's Il popolo d'Italia became an important voice among the leftist and democratic interventionist campaigners of 1914-15. His arguments even had an impact for some time on future Communist leaders such as Antonio Gramsci and Palmiro Togliatti. Eclipsed for a time because of his own absence in the army following intervention, the newspaper regained influence after the Italian military disaster at Caporetto galvinized public sentiment against defeat.
In the postwar period, Mussolini played heavily upon the interests of veterans, espoused the elitism of the Arditi (the Daring Ones) assault troops, and assailed the failure of parliamentary politicians to win the peace, i.e., the Italian war aims. On these elements, plus a shift to the employers' side of labor disputes, Mussolini began to build the Fascist movement.
Renzo de Felice, Mussolini, 5 vols, Turin: 1965-81
Denis Mack Smith, Mussolini: A Biography (New York: 1982)
Eric Palmer Hoyt, Mussolini's Empire: The Rise and Fall of the Fascist Vision (New York: 1994)