There are many different variations on fascism. We take the word from Mussolini's party but that does not mean that all regimes which might be described as fascist are all the same thing, and in many cases there is substantial dispute as to whether the term applies, not least because fascism is a very slippery concept.

George Orwell concluded that it was not easily definable in his short piece What is fascism? (1944). Umberto Eco expanded on the same theme 50 years later in his essay Ur-Fascism:

Italian fascism was the first right-wing dictatorship that took over a European country, and all similar movements later found a sort of archetype in Mussolini's regime. Italian fascism was the first to establish a military liturgy, a folklore, even a way of dressing – far more influential, with its black shirts, than Armani, Benetton, or Versace would ever be. It was only in the Thirties that fascist movements appeared, with Mosley, in Great Britain, and in Latvia, Estonia, Lithuania, Poland, Hungary, Romania, Bulgaria, Greece, Yugoslavia, Spain, Portugal, Norway, and even in South America. It was Italian fascism that convinced many European liberal leaders that the new regime was carrying out interesting social reform, and that it was providing a mildly revolutionary alternative to the Communist threat.

Nevertheless, historical priority does not seem to me a sufficient reason to explain why the word fascism became a synecdoche, that is, a word that could be used for different totalitarian movements. This is not because fascism contained in itself, so to speak in their quintessential state, all the elements of any later form of totalitarianism. On the contrary, fascism had no quintessence. Fascism was a fuzzy totalitarianism, a collage of different philosophical and political ideas, a beehive of contradictions.

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Fascism became an all-purpose term because one can eliminate from a fascist regime one or more features, and it will still be recognizable as fascist. Take away imperialism from fascism and you still have Franco and Salazar. Take away colonialism and you still have the Balkan fascism of the Ustashes. Add to the Italian fascism a radical anti-capitalism (which never much fascinated Mussolini) and you have Ezra Pound. Add a cult of Celtic mythology and the Grail mysticism (completely alien to official fascism) and you have one of the most respected fascist gurus, Julius Evola.

But in spite of this fuzziness, I think it is possible to outline a list of features that are typical of what I would like to call Ur-Fascism, or Eternal Fascism. These features cannot be organized into a system; many of them contradict each other, and are also typical of other kinds of despotism or fanaticism. But it is enough that one of them be present to allow fascism to coagulate around it.

Thalheimer's theory of fascism is also interesting in this context, taking its inspiration from Marx's observations of the previous century:

Thalheimer took as his point of departure Marx's analysis of the Bonapartism of Louis Napoleon in his "18th Brumaire of Louis Bonaparte." He was careful to apply Marx's method to the specific conditions of Europe after the Great War, and did not fall into the trap of confusing Bonapartism with Fascism, or of forcing his ideas into the mold of the "18th Brumaire." Yet Thalheimer saw striking similarities between Bonapartism and the rise of Fascism, similarities not merely outward and apparent, but grounded in the presence of certain specific classes and the historical relationship between these classes. The spectre of working-class revolt that threatened the position of the bourgeoisie in France in 1848 threatened the position of the German bourgeoisie in 1918/19. Parliamentary rule in France did nothing, according to Marx, to assuage the fears of the French bourgeoisie, which accordingly looked for a drastic political solution to their predicament: