The Weimar Republic!
Even though the Weimar Republic had a high point from 1924-1929, it was overall a failure and created the right social, political and economic conditions for the rise of extremist groups like the Nazi party.
There were many factors that contributed to the failure of the Weimar Republic of Germany. These included
The unresolved defeat of Germany 1918 in WW1- where the German government signed an armistice on behalf of Germany; many people felt that they had been stabbed in the back by these politicians as they thought they were winning the war.
Resentment against the government for the signing of the Versailles Treaty (meaning Germany carried the guilt for the war and had to pay back enormous reparations).
The forced struggle against the activities of the Nazi (then National Social German Workers) Party- like revolts and protests,
Inflation and an unstable economy and;
The basic lack of support for the Republic among the German people.
These aspects were the major causes which doomed the Weimar republic to ultimate failure and the rise of Hitler's nationalist party to power.
Up until 1918, the Kaiser had been running Germany as a military dictatorship. At the start of 1918, Germany was winning the war, but with America joining the allies, and German supplies running extremely low, Germany's fate changed quickly, and in June 1918, their major offensives had slowed, and then come to a holt. The allies then counter-attacked and with Germany to weak to defend itself, and their territory threatened- they had no choice but to make peace. The German army's position had changed so quickly, many people had trouble accepting that they were losing the war. The Allies offered peace on the condition that Germany got rid of the Kaiser- but at first, he refused...