Why did the Weimar Republic face opposition between 1919-23?

* The 'German Revolution' of 1918-19 had been very shallow, and the old elites were still firmly entrenched in key positions. * The Social Democrats (and liberals) were held responsible for the defeat in World War 1, and above all, for the armistice of November 1918. * The German Nationalists and the German military, who had been the warmongers, refused to accept any responsibility for their role in embarking on a huge gamble in 1914. * Instead of accepting any responsibility at all, the hardline nationalists peddled all kinds of conspiracy theories, such as the 'stab-in-the-back' legend, and talked of Weimar as a 'Jewish Republic', which of course it was not. * The harsh terms of the Treaty of Versailles. * Fear of Bolshevism. Please also see the related questions below.