Was Fascism in early 20th Century Europe born out of Socialism and how similar were fascist/socialist states in praxis?

Given that the answer linked covers mostly the German case I might try to say something about the Italian situation.

First though I need to clarify that, at least in my understanding, a comparison between socialist and fascist states in praxis is quite hard to develop. The main reason is the fact that you have a deep lack of theoretical foundation of a Fascist state, while a bunch of countries are often grouped together under this cover - Italy and Germany in primis but also Spain and "lesser" autoritharian governments - which brings to a remarkable difficulty in establishing what fascism is: should we look into the doctrine of Fascism? Should we value as definitive statements the ones contained in propaganda works - as for Hitler's Mein Kampf - even when never really developed in practice? Or should perhaps look at the many facets of the actual structure of the self-professed fascist countries?

Because it is almost self evident that the doctrinal part of fascism is opposite or at least mutually exclusive with regards to the main principles at the foundation of a socialist state. But it is also true that this doctrine has often - and moreso in the Italian Fascism - been developed after the rise of Fascism, with the explicit purpose of providing a third way between capitalism and socialism. It was meant to justify, explain and give a theoretical ground to the Fascist "success" especially following the crisis of 1929. It was not a pescriptive doctrine but a "descriptive doctrine". Fascism was already there.

On the other hand we have countless examples of Socialist Literature which predate the foundation of the USSR. Is it a good idea to compare our Fascist doctrine with the Socialist one? Should we limit ourselves to the contemporary doctrines?

Unfortunately this is beyond my possibilities given that my knowledge of the Soviet Union is quite limited to the basis. On the other hand this leads to another issue: we have one main, huge, socialist nation and a bunch of self-professed fascist nations. What is the range whitin we can move while still being in the Fascist region? And what is the range of Socialist nations?

Some days ago a question asked wether Spain was a Fascist nation under Franco's rule. Was it? If we set the divide at the border between Italy and Spain, than we can safely say that there were hardly any relevant elements in common between Italy and the USSR. Again I must wonder: are we disregarding points of contact for the sake of what was mostly propaganda?

Hoping that you will forgive this long introduction, let's focus on the rise of fascism.

In 1919, when the first Fascio di Combattimento was founded; Socialism was already a major player in the Italian politics. It had been since the Giolitti reform of 1912 which introduced universal suffrage. The PSI (Socialist Party of Italy) went from 7,4% in 1909 to 17,6% in 1913 to a staggering 32,3% in 1919 right after the war under the lead of Nicola Bombacci (who might be remembered by some because he was executed together with Mussolini in 1945).

The number of people allowed to vote had risen conspicuously, from less than 3 millions in 1909 to over 10 millions in 1919, and, despite Giolitti's hopes, this had not led to mass partecipation in the traditional parties but to the rise of new ones: the People's Party (ie the catholics led by Don Luigi Sturzo; 20,5% in 1919) and the Socialist Party.

Now, the key word here is new. The people who were born outside of the voting rights, were not looking to committ themselves to the old parties; they were looking for new perspectives and the Socialist Party was at the time the most appealing. But you should not imagine Italian Socialism as the monolithic structure that was projected abroad by the USSR since the late WW2. At the time of the rise of Socialism in Italy Lenin's idea of the party was confined to an extreme minority and Italian Socialism was shaped by Bakunin and Preudhomme as much as by Marx and Engels. This gave room to many different "social issues" and many different - even irreducible - solutions. For example a part of the socialist was open to cohoperation with a centrist government. Others stressed the fact that the solution of the social problems could rise by the breaking of the old empires. Others advocated violent revolution as the only way to fix society. Some spoke of the global proletarian revolution, others of the progress of the Italian Nation.

Specifically a huge number of future members of the Fascist Party, even founders of local Fasci di Combattimento as early as 1919-20, were active within the Socialist Party, including Arpinati, Farinacci, Rossoni, Grandi, etc. This should not be a surprise, given that the most interesting feature for many supporters of the Socialist Party was at the time its novelty (which brought many of them to see connections - which in strict doctrinal terms were absurde - between socialism and futurism) and the perspective of a decisive breaking with conservativism and the old values.

The lack of a precise direction - which gave room for a rapid and surprising growth - was bound to cause troubles inside the party. I won't follow the many break ups among the leaders which led to the foundation of currents or minor parties.

The most significant division appeared during the first world war, and was often cause of furthere fragmentation between pereexisting groups. For example the moderate - reformers - were open to support the government after the intervention, while the party statement was that of "neither support nor sabotage". Among the extreme left - revolutionair socialist - though a significant number had favoured the war entrance as the spark that was bound to cause the world revolution. Others simply believed that the fall of the "conservative" empires was destined to bring an improvement of the social condition of workers - as in more advanced countries like France and England.

Among these issues a man like Benito Mussolini thrived. Now, before I move forward I feel the need to briefly explain why...