Historically, these things happen quickly because they are harder to stop that way.

Dictatorship happens gradually, and then suddenly.

(With a hat tip to Hemingway, who described the process of going broke the same way)

I'm recommending Ruth Ben-Ghiat's new book Strongmen: Mussolini to the Present to people interested in reading a broad case study of the rise, reign and fall of dictators, because it is a 100-year survey capturing the similarities and some occasional differences.