The Treaty of Versailles in the mind of the Germans stabbed them in the back, especially the guilt clause that made them take blame for the First World War. Hitler capaitalized on these sentiments and used them to rally the German people.
Primary sources are the first hand evidence left behind by participants or observers at the time of events. Primary sources originate in the time period that historians are studying. They vary a great deal.
Historians use primary sources as the raw evidence to analyze and interpret the past. They publish secondary sources - often scholarly articles or books - that explain their interpretation. When you write a historical research paper, you are creating a secondary source based on your own analysis of primary source material. Examples of primary sources include diaries, journals, speeches, interviews, letters, memos, photographs, videos, public opinion polls, and government records, among many other things.