Known as Il Duce ("The Leader"), Mussolini was the founder of Italian Fascism. In 1912, Mussolini was a leading member of the National Directorate of the Italian Socialist Party (PSI), but was expelled from the PSI for advocating military intervention in World War I, in opposition to the party's stance on neutrality. Mussolini served in the Royal Italian Army during the war until he was wounded and discharged in 1917. Mussolini denounced the PSI, his views now centering on nationalism instead of socialism and later founded the fascist movement which came to oppose egalitarianism and class conflict, instead advocating revolutionary nationalism transcending class lines.Following the March on Rome in October 1922, Mussolini became the youngest Prime Minister in Italian history until the appointment of Matteo Renzi in February 2014.