As he was developing the fascist ideology during the war years, he continued to advocate "heroic action" but he now saw this in terms of military action rather than in terms of workers revolution. "Revolution is an idea that has found bayonets!" -- a slogan borrowed from the 19th century guerrillaist socialist Blanqui -- was enscribed on the banner of Mussolini's newspaper, Il Popolo d'Italia. He considered that the military struggles unfolding in Europe could have "revolutionary" consequences but saw this in terms of an improvement in the position of the Italian nation, as underdogs ("a proletarian nation") in comparison with the major imperialist powers such as Britain. (Note the similarity to the leftist ideology of "national liberation" -- in each case the interests of workers get subordinated to a ruling elite under the rationale of a nationalist fight against the imperialism of the major powers.)
Mussolini was an opportunist whose motivation was that of making his own personal mark on history. The weaknesses of Italian socialism and the nationalist fervor during World War I convinced him that nationalism was a more promising vehicle for his personal ambitions.
Nonetheless, Mussolini got very little support from the working class for his new patriotic, pro-war position. Working people in Italy had seen too many instances of troops and cops being used to repress workers struggles to identify the military as "theirs." However, Mussolini did succeed in convincing the main leadership of the Italian Syndicalist Union (USI) of his patriotic position by early 1915. At the USI's congress in 1915, its general secretary, Alceste de Ambris, and other leaders such as Filippo Corridoni, tried to sway the organization into a pro-war position. It is this event that gave rise to the myth of syndicalist support for Mussolini.
However, Armando Borghi and other anarcho-syndicalists were able to win the debate and the overwhelming majority of USI members rejected the arguments of the pro-war faction, who were only able to break out a few thousand members of USI to set up a new nationalist union, the Italian Labor Union (UIL). Mussolini's movement was mostly not built from within the working class, where anti-militarist sentiment was deeply rooted.
-- Tom Wetzel