It is impossible to avoid this question if you look at pre-World War II history. I have been researching this era for my current writing project, a sequel to The Better Angels. In the case of Germany, the loss of democratic norms and structures happened step-by-step, and it happened fast. For this post, I decided a list would suffice. Here it is: Ten months in Germany, 1933.
January 30: Hitler is appointed chancellor.
February 27: The Reichstag is set afire giving Hitler an excuse to arrest opponents without charges, dissolve political parties, and limit the press.
February 28: Hitler prevails on President Hindenburg to sign a decree suspending seven sections of the constitution guaranteeing individual and civil liberties including free expression, freedom of the press, rights of assembly and association, and privacy of postal, telegraph, and telephone communications. The decree also allows the Reich government to take power in the states.
March 5: The last democratic elections until after Hitler’s death are held. The Nazis win only 44 percent but carry on with a coalition government.
March 13: Joseph Goebbels is brought into the cabinet as “Minister of Popular Enlightenment and Propaganda.”
March 20: The first Nazi concentration camp, Dachau, is completed under the direction of Heinrich Himmler.
March 21: “Special Courts” take over cases of “political crime.” These courts consist of three judges, who are Nazi party members, and no jury. Hitler and Hermann Goering interfere in the judicial branch, quashing criminal proceedings against their friends and allies.

March 23: The Reichstag passes the Enabling Act giving Hitler absolute power, including the power of legislation, the approval of treaties, and the initiation of constitutional amendments. The Act passes 441 to 84. In the words of journalist William Shirer, the parliament “turned over its constitutional authority to Hitler and thereby committed suicide.”
April 1: Hitler proclaims a national boycott of Jewish shops.
April 7: The Law for the Restoration of the Professional Civil Service excludes Jews and political opponents of Nazis from civil service positions. This law will lay the foundation for the Nuremberg Race Laws of 1935.
April 11: By decree, Nazis define who is “non-Aryan.”
April 25: The Law Against Overcrowding in Schools limits the number of Jewish students in public schools. It is followed up by legislation curtailing “Jewish activity” in the medical and legal professions.
April 26: The Gestapo is established in Prussia.
May 2: Hitler outlaws trade unions. Their offices are raided, leaders arrested, and funds confiscated.
May 10: Organized book burnings are carried out throughout Germany.
July 14: All non-Nazi political parties are banned by law.
July 14: The Law for the Prevention of Offspring with Hereditary Diseases mandates sterilization of individuals with certain physical or mental disabilities.
July 14: The Citizenship and Denaturalization Law allows the Reich government to take away citizenship from “undesirables.”
August 30: The 5th Party Congress “Rally of Victory” kicks off in Nuremberg. Leni Riefenstahl directs her first propaganda film, The Victory of Faith, documenting the rally. At the following year’s rally she will film Triumph of the Will.
September 29: The Hereditary Farm law prohibits Jews from owning farmland or engaging in agriculture.
September 29: The establishment of the Chambers of Culture under Joseph Goebbels allows regulation of cultural activities and the exclusion of Jews from film, theater, music, fine arts, literature, broadcasting and the press.
October 4: The Reich Press Law makes journalism a “public vocation” regulated by law. All editors must be “Aryan.” Editors must not allow anything in the newspapers which is “misleading” to the public or tends to weaken the German Reich.
November 24: The Law against “Dangerous Habitual Criminals” allows courts to order indefinite imprisonment.
In 299 days—slightly less than ten months—all these events occurred. These events and more. For so many, their individual stories were never told. Whose shop was destroyed? How many Jewish doctors and lawyers were barred from their professions? Who was sent to Dachau in its early months? Who stood in the public square in Berlin and watched 25,000 books burning in a massive bonfire?