First of all, because there has been some confusion in this thread with /u/hankbaumbach and /u/NientedeNada about what Antifa is: While it is true that in the American context, Antifa as a movement has only received recent attention, groups under the label have existed since the 1980s and 1990s, especially the New York Antifa and while the longer roots of Antifa dated back to 1930s Germany, its immediate roots in the US overlap strongly with the Anti Racist Action, a lose network of groups founded in 1987 which is very much in the spirit of Antifa but chose Anti Racism as their moniker because in the American context back then Racism was a much more noticeable and understandable term than Fascism. It stretches the 20-year rule a bit but for more on the history of ARA and their fight against Racist groups before now, check out Beverly Peterson's 2000 documentary Invisible Revolution.

Antifa or the Antifascist Action (Antifaschistische Aktion) are a self chosen moniker for groups of antifascists that trace their roots back to 1930s Germany. The first group under this name was founded in 1932 by the German KPD in order to oppose the fascists thread rising in Germany but the term "antifascism" is even older an dates back to various activities in 1920s Italy and Germany. What is important about this part of their history is that the Antifaschistische Aktion and a variety of antifascist committees that followed it in Germany is that it was one of the few places where members of the communist party and members of the Social Democrats actively collaborated on a local level to stem the rising tide of Fascism despite their parties otherwise not getting along very well. This tradition was kept after WWII and the liberation of Germany when in many a local these Antifascist Committees sprang up again in order to help and pressure the Allies to denazify Germany and arrest various Nazi criminals. After the immediate post-war, most of these groups went dormant until the label was reactivated in the 1980s by the autonomous, squatter, and anarchist punk scene in order to fight the reemerging Neo-Nazi scene in Germany and elsewhere. While there would be more to say about this history, in essence it is this revival of the label and of certain aesthetics and tactics that we associate today with Antifa and that had a particular hey-day in Germany after the resurgence of Neo-Nazism after re-unification. As I said, I could take more about this history but maybe that is best left for another post as to not detract too much from the question here.

So, as for the question here: What has smothered nascent fascist movements and has violence played a role. The problem with finding a general answer here is that a.) it is really hard to distill this down into a very general and widely applicable answer since it is hard to determine where a nascent movement of Fascists was smothered and wasn't allowed to grow in the long run because of some problems with counterfactuality and b.) that a historical "How to guide" on defeating Fascists movements is hard to do because of the very different historical context in many a ways.

What I mean by that is that e.g. in Germany with the reemerging Neo-Nazi movement of the 1980s, Antifa was often successful in denying them a public platform as well as preventing them from exacting violence. Such was the case in August 1992 in Rostock-Lichtenhagen, when several hundred Neo-Nazis under the cheering eyes of 3000 onlookers, who also interfered with the insufficient police force, started a pogrom against refugees in Rostock and Vietnamese Laborers housed there. Their living quarters were set on fire and the Vietnamese there were left to their own because police retreated. In the following days, Antifa activists were sometimes successful where the police was not in preventing further violence against visibly foreign people in Rostock but even today, many activists say that they should and could have done more.

But on the whole, it is still the case that Nazism is outlawed in Germany and that the German state will actively prevent the foundation of a new Nazi party and outright Nazi demonstration. It is only in the grey zone of not being outright Nationalsocialist that Neo-Nazis in Germany today are allowed to march in public and so forth. And where they have done that, they have encountered resistance that sometimes has been successful such as in Dresden where coalition building between Antifa and non-Antifa and intervention by Antifa has succeeded in stopping the Neo-Nazis remember the bombing of Dresden marches.

It's difficult to gauge if this "smothered" Fascism in Germany or not because, as I said above, the state does intervene too in that it outlaws outright Nazism in Germany but it is certainly a success in a larger sense that they have been denied a public platform and that, as was the case in 1992, at least some of the violence the Neo-Nazis wanted to exact had been prevented.

Historically, there have been examples of an intervention from the left stopping actual Fascism. In 1920 in Germany the so-called Kapp Putsch (Kapp coup) occurred when extreme right military officers tried to seize power in Germany and the coup was stopped by the SPD calling a general strike and armed workers in Berlin clashing with Kapp's troops. Kapp's government couldn't function because of the strike and the armed clashes lead to him being on the losing side so that ultimately he had to flee. But again, this is an example from a very specific context and both without an historical situation where a coup is threatened and occurs and where there is a mass party able to call for a general strike and armed insurrection by its members, the strategy used against Kapp can hardly serve as a general example on hos to defeat fascism.

In terms of 1920s and 1930s street fighting in Germany between Social Democrats, communists, and Nazis we are now acutely aware that these fights were unable to stop the Nazis from seizing power but as historian Oliver Reschke pointed out in a 2014 lecture based on his doctoral research on street fighting in Berlin, the areas where the left was most successful in fighting the Nazis for street and other presences – often violently – where the areas which showed the lowest support for the NSDAP at the ballot box while traditional workers' areas where the fight was less successful – in part due to the police being supportive of the SA – were generally more supportive of the Nazis at the ballot box. Again, the question is how applicable that is for a contemporary context since back then there were two massive party structures behind these fights.

I could go on with such things as the failed uprising of Social Democrats in Austria against Fascism and others but I think the gist of it is that while denying Nazis and Fascist public space, if necessary physically, has historically been sometimes successful in terms of localized examples and in terms of drawing attention to the problem, smothering Fascism is something that involves both civil activists as well as the state and its might in terms of taking steps necessary to protect the order and values on which democracy is built. In short, despite grander claims of some Antifa groups of being successful in fighting Fascists, their success was in most historical cases one of the localized variety while in terms of a society wide level, it was partly down to state action and broader coalitions of people who opposed Fascism.

Sources aside those mentioned:

• Jochen Schmidt: Politische Brandstiftung. Warum 1992 in Rostock das Ausländerwohnheim in Flammen aufging..

• Christin Jänicke, Benjamin Paul-Siewert (Hrsg.): 30 Jahre Antifa in Ostdeutschland. Perspektiven auf eine eigenständige Bewegung.

• Birchall, Sean (ed.). Beating The Fascists: The Untold Story of Anti-Fascist Action..

• McElligott, Anthony: Weimar Germany.