Fascism was a philosophy and political ideology originally developed in Italy at the beginning of the mid-20th century by Benito Mussolini. In the 1930s this ideology became a government style after Adolf Hitler took power in Germany and established the Nazi state. (TOS: "The City on the Edge of Forever").
A key pillar of fascism was the so called "Leader Principle" which stated that a government should have a single leader as its head, with all others obeying this leader without question. In the 20th century fascist leaders were generally deemed evil and psychotic men and it was for this reason that fascism failed on Earth as a viable form of government. However, even in cases where a fascist leader governed for the good of the people, it was a fact that when any man held so much power then it was in turn irresistible that an urge to "play God" would corrupt the government. Such was the case on Ekos, where Federation historian John Gill founded a peaceful fascist government only to have his government turn evil just like its predecessors. (TOS: "Patterns of Force")
The structure of the Cardassian Union is very reminiscent of historical fascist empires, with its extreme devotion to the state and the Cardassian Articles of Jurisprudence, which assume guilt prior to trials.