In the wake of the First World War, “Fascism” appeared to be a new political form on the march toward power. It challenged both the decrepit Liberalism of the Nineteenth Century and a revolutionary Bolshevism. Benito Mussolini’s Fascist Party came to power in Italy in 1922. Copy-cat movements appeared in many other European countries. For the most part, these movements arose in backward countries that emerged from of the collapse of the great empires at the end of the First World War. Often, their rise met their limits in the willingness–eagerness in some cases–of the traditional forces of order to shoot people who clamored too loudly.
Then came the Great Depression. The political systems of a host of countries ground to a halt over “distributive contests”: cut taxes or raise taxes, cut public spending or raise public spending, and for whose benefit? Fascist movements arose or gained numbers in Belgium, Ireland, Spain, France and Britain. Most importantly, Germany’s democratic Weimar Republic collapsed and Adolf Hitler came to power. In the United States, some people on the right saw the New Deal’s inflationary monetary policy, the elaboration of government controls on business, and Franklin D. Roosevelt’s “cult of personality” as steps toward an American fascism. On the left, many people saw the populist campaigns of the “demagogues” Hughie Long and Father Coughlin as fascist threats to democracy. Happily, by 1945, such fears had passed. Fascism had been destroyed and discredited.
Yet the idea didn’t disappear. Robert Penn Warren’s novel All the King’s Men (1947) and the movie of the same title (dir. Robert Rossen, 1949) were based on Long as a demagogic threat to democracy. Long also partly inspired “A Face in the Crowd” (dir. Elia Kazan, 1957). It is often discussed as an examination of the populist demagogue who is contemptuous of his followers. A very different approach came in the novel by Fletcher Knebel and Charles W. Bailey II, Seven Days in May (1962) and the film of the same title (dir. John Frankenheimer, 1964). Here the danger came from right-wing military officers opposed to arms control.
Since the 1960s. the term Fascism became “a political expletive.” not an “investigative concept.” In the Sixties it was a rhetorical rock thrown at Republicans and the police. In the early 21st Century, the American right used it to describe a changed liberalism. The election of Donald Trump, well ahead of any policies he pursued, immediately aroused denunciations of Fascism from the left. Despite 6 January, American democracy remains strong—if stalled.
 The nature of Mussolini’s grip on power was much misunderstood in Western democracies at the time. Fundamentally, he had compromised with powerful conservative institutions: the army, industrialists, great landowners, and the monarchy. Mussolini got the trappings of power and the opportunity to build something more, while conservatives got a suppression of the Left. See: R.J.B. Bosworth, The Italian Dictatorship: Problems and Perspectives in the Interpretation of Mussolini and Fascism (1998).
 F.L. Carsten, The Rise of Fascism (1969) is a good guide to developments as understood by historians before the subject became over-theorized.
 See: on Rumania Iron Guard – Wikipedia; on Bulgaria History of Bulgaria (1878–1946) – Wikipedia; on Weimar Germany’s “Beer Hall Putsch” Beer Hall Putsch – Wikipedia
 See Sinclair Lewis, It Can’t Happen here (1936), a sort of instant-book intended to help derail Long’s pursuit of the presidency. Carl Weiss got there first.
 See, for example, Jonah Goldberg, Liberal Fascism: The Secret History of the American Left, From Mussolini to the Politics of Meaning (2008).
 Bruce Kuklick, Fascism Comes to America: A Century of Obsession in Politics and Culture (2022).