Typically in sociology and political science, the radical right has been addressed through so-called breakdown theories, while left-wing radicalism has been analyzed from the perspective of mobilization theories, which are widespread in social movement studies. For a long time, especially in the United States, unconventional forms of collective action were identified as crisis behavior. Considering collective phenomena as the sum of individual behaviors, psychologically oriented theories defined social movements as the manifestation of feelings of deprivation experienced by individuals, with aggression resulting from a wide range of frustrated expectations. Phenomena such as the rise of Nazism, but also more contemporary movements, were considered as aggressive reactions to frustrations resulting either from a rapid and unexpected end to periods of economic well-being and of increased expectations on a worldwide scale or from status inconsistency at the individual level. This type of approach resonated with interpretations of the extreme right as non-reflected reactions to social crisis and unsuccessful integration.
Caiaini, Manuela and Donatella della Porta. 2018. "The Radical Right as Social Movement Organizations." In The Oxford Handbook of the Radical Right, ed. Jens Rydgren. Oxford: Oxford University Press, 327-347. https://books.google.com/books?hl=en&lr=lang_en&id=XD9FDwAAQBAJ&oi=fnd&pg=PA327&dq=%22Donatella+della+Porta%22&ots=m6fVeAKrpi&sig=cHoQwLQI4IuD3Ip1BKnwseyGv3Y#v=onepage&q=%22Donatella%20della%20Porta%22&f=false