The Nazi's believed that the Weimar Republic was weak, and that a single strong leader was needed. They believed that Germany's defeat was caused by wealthy Jewish bankers who had withdrawn support for the war and were behind the Treaty of Versailles.
The Nazis wanted to create a higher order of Germans. They followed the idea of "Social Darwinism". They believed that the Aryans (people with blonde hair and blue eyes) were superior, or the "Master Race", while the Jews were considered "sub-human". They even based their 25 point manifesto on the idea that Jews are inferior, and that they didn't deserve any of the rights that Germans were entitled to.
Many of the points in their 25 point plan were very subtly worded attacks on Judaism. For example, point 4 states that "Only a member of the race can be a citizen. A member of the race can only be one who is of German blood, without consideration of creed. Consequently no Jew can be a member of the race." This is saying that Judaism is a race, not a religion, and that they could not be a German citizen.