The period that immediately followed World War I was marked by the fall of the German, Russian, Austro-Hungarian and Ottoman Empires. Basically, the governments were gone, and the people were left in total desolation. Economically, many people were ruined because wars are expensive, wars destroy workplaces, and war leaves many soldiers unemployed after the fact. .
Democracy failed in the post-World War I world mainly because it was unable to allow for economic viability. It was impossible for everyone to have a say in the government of the countries, and establish some sort of economy that would keep people from starving. Promises were made by Hitler and other fascist leaders that their rule would lead to greater gains to all people. These promises, true or false, led to a wave of totalitarianism governments and seemed to be the "newest thing".
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The rise of totalitarian governments led to the rule of Adolf Hitler, which of course led to World War II. Under Hitler, as with any totalitarian government, the people are dependent totally on the whims of one political party, and one leader. Both Italy and Spain had totalitarian systems before Hitler - with Mussolini in Italy being the first to implement the system. .
Hitler was able to build up Germany economically and militarily because of his promises to overturn the Treaty of Versailles, and his promise to secure more land for the Germans. His ideas were racist, of course, but were turned to as the depression hit Germany full-force in the early 1930's.
His great speaking ability caused him to become a popular leader among Germans. He was quick at securing his supreme power after being named Chancellor on January 30, 1933 - he banned Communism, and passed the Enabling Act, which granted the government power over all aspects of German life. He became head of the state after the President died in 1934. He combined the legislative, executive, judicial and military authority, and then assumed the authority himself.