Fabian Socialism is the explicit and dedicated effort to subvert non-Socialist society by subversion, infiltration, and a kind of long-march through the institutions; such that society can be slowly molded or pushed into the Socialist order, without the need for a bloody and violent revolution upfront. The revolution can be delayed while Fabians lay the groundwork for it, so that the revolution is inevitable. This slow war of attrition is where the name "Fabian" comes from. It is a reference to the name of the Roman general who defeated Hannibal by refusing to engage in pitched battles with him, wearing down his supplies, and training his troops to gain experience in small skirmishes until Hannibal was effectively out-maneuvered and forced to leave Italy.

Fascism arises as a form of "Organized, Italian, Trade Unionism" as Mussolini leaves the Socialist Internationale, because they refuse to understand that Nationalism should be fully adopted by Socialists to gain power. The Fabians have already been using Nationalism as a mechanism to divide up the European monarchies into, literally, balkanized ethno-states vying for power and position. The Fabians were favoring the Mensheviks and Trotskyists in the Russian Civil War, but Lenin and Stalin had isolated both out from power, meaning that their preferred winner was now out of the picture in the Soviet Union. The SDP (Social Democratic Party) in Germany did win the 1918 Revolution, so the Fabians had subordinates in Germany, but not Russia.

Fascism (or State Syndicalism, or Corporatism), takes the entire economic structure of society and pumps it through the state, and corporations (national unions) are monopolized into massive state supported industrial cartels that set prices, fix wages, and otherwise run the economy from the top; without actually having a government bureaucrat set a price. That is what the Communists in the Soviet Union were doing, they had never really improved their economy, and were instead slaughtering everything that moved. Fascism looked like it was appealing to the Fabian agenda, despite being revolutionary in nature anyways.

Fascism actually appeared to be quite "progressive" for it's time. It explained itself as more competently run, more technocratic, more scientific, more 'evidence-based', in such a way that it would have all the social benefits of Socialism, with all of the economic benefits of Capitalism. The truth is: Fascism was often touted, economically, as a centrist position. Or a "third way" or "third positionism".

Many Progressives and Fabians actually thought it could be a very good idea for how to run a country. Fascism actually had a good bit of support from the intelligentsia. Mussolini was actually regularly praised by Franklin Roosevelt, and Maynard Keynes (a very important economist of the time). Keynes himself invented a completely different concept of money and monetization in an economy, and explicitly stated that his monetary policy would work best under Fascist systems where government control was absolute.

When Adolf Hitler's NSDAP started to gain power in Germany, it brought the rule of the SDP (the Fabian's acolytes) into jeopardy. It was originally Mussolini and Fascist Italy who were tapped as a potential counter to German Adolf Hitler, even going so far as to deploy Italian troops to the border of Germany at the behest of the west. National Socialism and Fascism are not interchangeable, and are actually a bit different on some crucial points (including race). It was actually Hitler's diplomacy which brought Italy onto his side before WW2 started.

The Left now desperately wants to bury the fact that some of their most cherished politicians and economists were quite fond of Fascism, and that the system they built is explicitly designed to be at it's most effective state in a Fascist environment. But the truth is that, at one time, for several decades, Fascism was a progressive ideal.