The correct answer is C. Fascism.
Step-by-step explanation
A radical authoritarian nationalism refers to a political, social and cultural system that seeks to exalt the national identity to make a nation prosperous, usually through one political party that has all the power to govern and even controls the way of life of the population. During the early 20th century a radical authoritarian nationalism called fascism emerged, this was a European political movement that began in Italy during the mandate of Benito Mussolini, which was characterized by being authoritarian, promoting national unity and exalting national identity to have a strong nation. So, the correct answer is C. Fascism