De Felice's leading interest was in Fascism. In his view, there were two types of Fascism, "Fascism as a movement" and "Fascism as a regime". De Felice saw Fascism, especially in the "movement" stage, as a revolutionary middle-class ideology that had deep roots in the Age of Enlightenment. Moreover, De Felice insisted that it was not caused by fear of a proletarian revolution on the part of the lower middle classes, as leftist historiography maintained; but it was an assertive movement, originated by an emerging middle class in search for its proper role.