>>17950928 (OP)
The Italian fascists called themselves fascists. It comes from "fascio" which means league/group and political groups in Italy would use the term. The fascists began as the "Italian Combat Leagues" (or Fasci Italiani di Combattimento) which was a paramilitary war veterans group. Taken literally it can mean something like League-ism or Unity-ism. The vibe is all about unity, like in that poster, you see the fist closed around the sword. The individual fingers are stronger as a closed fist. The bundle of rods from the ancient Roman fasces are bound up together. It appealed to nationalistic Rambos who were hardened by their experiences on the front during World War I.
As to the "how," the hardening experiences of World War I. And also coupled with rapid economic change / industrialization that was going on. Europe was undergoing the transition from a horse-drawn to horsepower civilization. Rapid social change can often produce new divisions in society which appears like a bunch of different groups that are hostile to each other. So the fasicsts were all about unity. Everyone is going to serve the nation. The Italian fascists saw themselves as modernizers and were enthralled by technology like the airplane, but Italy as a single nation was a relatively new concept. The regional dialects there can almost be like different languages.
Also you can see how this would be appealing to soldiers and a war-like context. In the military, everyone has a place to be and a job to do:
https://youtu.be/TryfqARSEd4