Why horseshoe theory is nonsense
More useful ideas include:Confusionism: This term originates in France and is used in the UK by Andrew Coates and can be defined as the phenomenon that leads on certain subjects groups and individuals belonging to a priori opposite spectra of the political field to ally for opportunistic reasons but also because they arrive at these specific subjects to find and develop common ideological bases.
Querfront, German for "transversal front") has been described as "a recurrent motif in far-right thought over the past century. Craving the legitimacy that an alliance with progressive forces can provide, reactionaries seize on ostensibly shared positions, chief amongst them opposition to corrupt élites, to create the impression that progressives could benefit from making common cause with them." (See
here for more.)
Red-brown alliance: Like Querfront, this term originates in interwar Germany when Communists (going through their ultra-left Third Period, when they denounced Social Democrats as "social fascists" allied with the Nazis - leading to the war-time Molotov-Ribbentrop pact between Nazi Germany and Stalinist Russia) although there are earlier examples.
This important blogpost exhaustively details the history, including Strasserism (the purportedly working class socialist Nazi current purged during the Night of the Long Knives) and National Bolshevism.
Unorthodox fascism: This is the term used by Spencer Sunshine for left/right crossover movements such as new forms of Third Positionism, Julius Evola's influence, popular mobilizations against finance capital, conspiracy theories, Sovereign Citizen pseudo-legal theories and fascist neofolk music - see his forthcoming book of the same title.
Fascist creep: This is the term used by Alex Reid Ross that can be described as the creep between fascism and leftism, "the disturbing attraction many 20th-century leftists felt for reactionary ideology", often based on "nostalgia for [a] precapitalist 'lost paradise'" - see his book of the same title.
The big neo-Nazi crib: Finally, Croatian antifa activists have documented what they call "the big neo-Nazi crib", where fascists have rebranded by copying antifa iconography and re-purposing it. I've pasted a few of their examples at the end of this post.