The Weimar republic ended with the machtergreifung by the Nazis. This has obviously led to Weimar democracy being bot much derided and debated. Where exactly did it go wrong. Ironically, the Nazis themselves hated Weimar democracy, but virtually everybody now seems to agree that their alternative was worse.
In a way the Weimar republic got off to a bad start. The Allied powers had forced the German government to kick out the Kaiser and then to except the Treaty of Versailles. They created a republican government which immediately had to discredit itself.